SCEEUS Commentary No. 17
Executive Summary
Since spring 2025, Western security guarantees for Ukraine have become prominent in the public debate and political planning related to the end of the Russo-Ukrainian War. The points 5 of the November 2025 joint US-Russia s0-called “peace plan” and following 28-point counter-proposal by Britain, France and Germany say that Ukraine should receive “reliable” or “robust” security guarantees. These documents and the related public debate have brought the question of what such guarantees can mean to the limelight again.
Over the last year, the idea of a European “reassurance force” for Ukraine, to be supported by a US “back stop”, once a ceasefire has been achieved, has taken centre stage in this discussion. The readiness of several European countries to seriously consider deployment of ground troops to Ukraine and warships to the Black Sea marks a change in western perceptions of Ukrainian defence needs, which are now seen as part and parcel of all-European security interests. In spite of the progressive nature of the novel approach, and its positive reception in Ukraine, the idea of a larger reassurance force faces political and strategic challenges. Although its problems are distinct from those of a – less frequently discussed – UN peacekeeping mission to Ukraine, they are also grave. The prospect of a reassurance force has made Russia’s negotiating position less flexible, as the Kremlin is strictly against the deployment of any troops from NATO member countries in Ukraine. Moreover, should western ground troops and warships be deployed to Ukraine, it is unclear how the sending countries would behave in case of a re-escalation that drags the reassurance force into the Russo-Ukrainian War.
For these and other reasons, the remaining relevant aspect of a reassurance force concerns the deployment of European air forces to help Ukraine with the creation of either air protection zones over certain critical targets, such as key cities, embassies, rail- and highways, ports or nuclear power plants, or of a s-called Integrated Air Protection Zone over most of Western and Central Ukraine, as outlined in the so-called SkyShield initiative. Operating far away from the frontline and the Russo-Ukrainian border, western interceptors would only be shooting down Russian uncrewed aerial vehicles. Such direct support should begin before any agreement on a ceasefire, thereby helping to increase pressure on Russia. Optimal European military support for Ukraine before and after achievement of a ceasefire would be largely similar. After the high-intensity warfare ends, western delivery of modern weapons, intense military-industrial cooperation, intelligence sharing, combat training and assistance with air protection should continue or expand. Resolute European material and cognitive support for the Armed Forces of Ukraine, after achievement of a ceasefire, would appear to be a more realistic approach to implementing security guarantees than a tentative deployment of ground troops and warships as part of a reassurance force for Ukraine.
Introduction
The construct “security guarantees” has in recent months become a buzzword in international debates on western support for Ukraine. After the conclusion of a ceasefire, guaranteeing Ukraine’s security will be a central part of future foreign help to ensure the country’s survival. Current frequent use of the label, however, often occurs as part of arguments that leave key future political and strategic challenges undefined.
Benjamin Tallis notes that the concept of “security guarantees” can be misleading. A full guarantee of security is an unachievable mirage not only for Ukraine, but for anywhere. In the expert discourse, distinctions are made between guarantees and (weaker) assurances, as well as between positive and negative guarantees. Usually, a positive security guarantee, the kind of promise that Ukraine is aiming for, implies strong commitments by the provider on the protection of the receiver.
Diverging definitions and interpretations of security guarantees, as well as various ambiguities and contradictions in their planning present a problem. Open questions need to be identified from the outset. Frankness would help move from merely discursive progress concerning Kyiv’s future defence needs to achievement of material improvement in Ukraine’s security situation. This report tries to assess the difficulties in the most far-reaching suggestion that has been made in the discussions on Ukraine’s security guarantees – the deployment of foreign troops on Ukrainian soil.
The report’s three sections outline different conceptualisations of security guarantees in general and for Ukraine in particular, and certain strategic paradoxes concerning their implementation on the ground. The conclusions suggest possible solutions to some open questions and make recommendations for action to national, NATO-affiliated and EU-level policymakers in the so-called Coalition of the Willing (CoW).
The report assumes that Ukraine’s accession to either NATO or the EU is unlikely in the near future. Full membership of both of these organisations will come eventually, resulting in far-reaching security guarantees for Kyiv and fundamental improvements in Ukraine’s international embeddedness. For now, however, accession to NATO and the EU is not available as a mean of rapidly improving protections for Ukraine’s population and territory.
Who Makes Which Commitments to Whom?
While security guarantees have been intensely discussed in Europe and beyond throughout 2025, the specifics of future commitments, actions and coordination remain unclear. Unless these issues are resolved in advance, there is a danger that the promises that the term “security guarantees” seem to imply will not be fulfilled. Inconsistent implementation of apparently announced support and defence commitments would not only be dangerous for Ukraine. It would further undermine the already shaken European Security Order and rules-based international system.
One source of misunderstanding of security guarantees is their association with peacekeeping under the umbrella of an international agreement and/or organisation – above all, through UN-organised multinational troops. Indeed, a deployment of foreign forces on Ukrainian soil could increase Ukraine’s security. However, the deployment of UN or other neutral troops would, in the current context of the Russo-Ukrainian conflict, be the wrong type of armed assurance for Kyiv, even after conclusion of a durable ceasefire.
Until 2021, a deployment of multinational forces from third countries to the territories of the Donetsk and Luhansk so-called people’s republics might have made sense, in order to make the contradictory Minsk Agreements of September 2014 and February 2015 work. Today, however, since the expansion and intensification of the conflict almost four years ago, a classical international peacekeeping operation is a different matter. Since February 2022, the nature of the Russo-Ukrainian War has changed – and so have the conditions for the presence of foreign troops on Ukrainian soil in the event of a ceasefire.
First, UN or other armed peacekeepers deployed to secure a contact line that is incongruent with the Russo-Ukrainian border would be a normative, political and legal problem, in view of Moscow’s official annexation of Ukrainian state territory. Although, as a permanent member of the UN Security Council, Russia is obliged to implement the UN Charter, Moscow would use its veto power in the Security Council or at another negotiating table to protect its own national-imperial interests rather than those of the international community.
In any agreement on a peacekeeping operation, the Kremlin would only agree to a form of troop deployment by third countries that would protect or extend its territorial gains. As a result, with a peacekeeping operation that goes beyond an observer mission on the officially annexed territories, the United Nations or another third actor be would helping to protect the fruits of Russia’s expansionist war and support Moscow’s repressive occupation, as well as its russification campaign in the captured Ukrainian areas. The peacekeepers would be participating in Russia’s trampling of basic principles of the UN Charter – territorial integrity and the national sovereignty of its member states.
Second, in the case of a new escalation and resumption of Russia’s advance into Ukraine, few would expect neutral troops under the UN or another umbrella to be able and willing to fight one of the world’s largest conventional and nuclear military powers. Nonetheless, a readiness and capability to effectively contain movements by the Russian armed forces, and to thereby deter it from doing so would be the major task of a hypothetical peacekeeping force in Ukraine. Neither Kyiv, nor Moscow, nor any third parties would believe in a more than symbolic relevance of neutral UN or other peacekeepers in soothing a re-escalating Russo-Ukrainian conflict, however. It is thus unclear what the purpose of a classical peacekeeping operation would be.
Third, it is true that a heavy Chinese participation in such a mission could increase the status of possible UN or other multinational forces in Ukraine and would restrain Russia from engaging them militarily. Unfortunately, however, Beijing has provided increasing diplomatic, political, economic and technical support for Moscow since the start of the Russo-Ukrainian War in February 2014. As a result, there is today little trust in Kyiv and among its Western partners in a constructive engagement by Chinese troops that would respect Ukrainian territorial integrity and sovereignty, fully abide by international law and support an as just as possible peace. Instead, the suspicion would be that blue helmets from China would not behave as peacekeepers but instead function as proxies of the informal Russo-Chinese anti-western alliance on the territory of the pro-western Ukrainian state.
Against this background, the occasional discussions on UN or other international peacekeeping troops – going beyond an observer mission – along a future contact line as an instrument or even panacea for resolving the Russo-Ukrainian conflict are a distraction. One effect of intensely debating this currently irrelevant idea might be to prolong Russia’s ongoing negotiation theatre. At least in current conditions, this discussion does not contribute to identification of a realistic path to a sustainable solution of the conflict and achievement of durable peace.[1]
The Vagaries of a Western Reassurance Force
A more constructive approach to guaranteeing the stability of a future ceasefire is contained in the European idea of a “reassurance force” for Ukraine, which emerged in the spring of 2025. It implies, among other things, several thousand – or even a few tens of thousands of – ground troops deployed on Ukrainian territory, as well as a number of warships sent to the Black Sea by the more forward-leaning members of the CoW.[2] The ground troop contingent of the reassurance force would largely come from Western European members of the CoW, to be stationed at Kyiv’s invitation in western Ukraine.
This land operation would be the central part of a larger effort by the CoW to stabilise any future ceasefire. It would rely on a so-called US back-stop, meaning the provision of limited assistance to the reassurance force from afar. This US support would include air power, intelligence sharing and logistics capabilities but no US troops on the ground.
The current planning for a reassurance force in Ukraine in several major European capitals marks a fundamental change in Western attitudes to the future of Ukrainian security that has been welcomed in Kyiv. However, the of itself laudable European plan for a reassurance force in Ukraine suffers from two strategic paradoxes.
First, current Western public discussion of and planning for troop deployment in Ukraine is counterproductive for the ongoing Russo-Ukrainian negotiations on a ceasefire. The idea of a European reassurance force is rejected in Russia as strongly as it is welcomed in Ukraine. Since the first Western signalling of a readiness to send troops to Ukraine in the spring of 2025, Putin and other representatives have repeated earlier warnings that Russia would not accept any foreign forces from NATO member countries on Ukrainian soil.
Evaluating this situation in September 2025, the prominent Ukrainian journalist, Vitaly Portnikov, stated on the Espreso television channel that a peace agreement with Moscow would only be possible, if at all, if no foreign troops (except those of or approved by Russia) were allowed on Ukraine’s territory: “Russia will not sign any other version of a peace treaty. There are no tools that would force the Kremlin to agree to the presence of NATO troops in Ukraine. Either western countries dare to act while the war is still going on, disregarding Moscow's opinion, or it will never happen”.
While the debate on a reassurance force is having positive repercussions for Ukraine’s conceptual integration into trans-European security planning, its parallel strong rejection in Moscow has negative immediate effects on the negotiations of a ceasefire. Thus far, discussion of a Western reassurance force in Ukraine has made achievement of a compromise-based truce with Russia more distant. It has heightened the Kremlin’s stake in the Russo-Ukrainian War and thereby increased the amount of economic as well as military pressure on Russia required to persuade the Kremlin agree to a ceasefire.
Certainly, the idea of a European reassurance force is normatively laudable, strategically pertinent and politically justified. Such troops would not only contribute to the protection of Ukraine but also strengthen the European Security Order and global rules-based system. In view of its effect on the Kremlin, however, the plan’s official announcement was premature – even more so as the planning, logistics and financing of even a moderate reassurance force represents a considerable challenge. It is no wonder that the exact type, size and composition of a hypothetical West European troop contingent in Ukraine, as well as its rules of engagement remain unclear.
The plan’s second strategic paradox stems from the lack of clarity regarding a worst-case scenario in which the reassurance force would be dragged into active combat with Russia’s military. The trickiest question for any eventual deployment of Western ground troops in Ukraine would be what they would do if attacked by, for instance, Russian missiles or drones, leading to significant human and material losses. The reaction to such an incident would not just be a strategic conundrum – it would also have political implications.
A counterattack by the reassurance force that would mirror Russia’s attack would be the most appropriate answer from a military viewpoint and be the operationally apt response. However, a matching reaction that appears justified from a battlefield perspective woud have far-reaching consequences for the foreign, security and domestic affairs of the troop-contributing countries involved. A Russian attack and subsequent counterattack could start an escalation spiral that draws the troop-contributing countries, NATO and/or the EU into the Russo-Ukrainian War.
In the opposite scenario of no reaction by the troops of the reassurance force to a Russian attack on them, the strategic implications would not be as urgent but would be nearly as grave. A lacking or insufficient response to a Russian armed provocation with a high number of casualties would call the mission of the reassurance force into question, make it a sitting duck and demoralise the deployed soldiers. A meek answer would also have wider implications for the credibility of the Western security guarantees given to Ukraine as a whole. It would even call into question the mutual aid commitments formulated in Article 5 of NATO’s Washington Treaty and Article 42.7 of the Treaty on European Union. A similar strategic conundrum would arise regarding the deployment of and an attack on warships sent to the Black Sea in order to secure Ukraine’s government-controlled coastline and Ukrainian foreign maritime trade.
The SkyShield Plan
There is nonetheless a type of direct military assistance that the CoW could provide beyond mere material, financial and informational aid to the Ukrainian armed forces. While the deployment of ground troops or warships is fraught with strategic dilemmas, a limited engagement by the air forces of the CoW’s forward-leaning members over and in western and central Ukraine would be less problematic. Such support – which has been labelled SkyShield – would be possible and useful not just after agreement on a ceasefire but already before it, i. e. under current conditions.
A Western initiation of support for Ukraine by setting up certain local air protection zones or a larger Integrated Air Protection Zone (IAPZ) would constitute direct military involvement by select European countries in the Russo-Ukrainian War that goes beyond the current indirect military assistance provided to Kyiv. However, implementation of joint Ukrainian-CoW IAPZ or air protection zones over crucial cities such as Uzhhorod, Lviv and Kyiv, certain critical infrastructure such as highways, ports, gas storage and railways, as well as nuclear and other power plants would entail fewer escalation risks than the deployment of ground troops on Ukrainian soil or of warships in the Black Sea. European interceptors helping Kyiv to implement air protection zones or IAPZ could have their missions constrained in two ways.
First, Western engagement in Ukraine’s air defence should be designed to function only over limited Ukrainian areas far away from the current combat zones and the Russia-Ukraine border. Western soldiers over or on Ukrainian territory might be attacked by Russia from the air, in the same way as could happen to the ground troops and warships of a reassurance force. In such a case, however, the combat mission of the deployed Western interceptors, on the one hand, and their self-defence, on the other, would be largely congruent – disabling drones, cruise missiles and rockets flying from Russia into Ukraine.
Second, the geographic limitation of the COW interceptors’ mission to Ukraine’s rear, in central and western Ukraine would mean that they would not encounter any Russian manned aircraft or helicopters. Western interceptors, anti-aircraft drones and missiles would only be shooting down Russia’s unmanned aerial vehicles. No Russian soldiers or civilians would be harmed, and no Russian state territory would be violated in such a functionally constrained operation by European interceptors, far away from the frontline and the Russia-Ukraine border.
Such activity by a limited contingent of European soldiers (pilots, communication officers, technicians) near the border of, over and partly on Ukrainian territory could be justified in their homelands and vis-à-vis Moscow, as well as the larger international community as protecting the legitimate self-interest of the sending states. First, the embassies of the CoW countries in Kyiv are, under the 1961 Vienna Convention on Diplomatic Relations, their inviolable territories, and host diplomats as well as other governmental employees who need physical and psychological protection. Second, the recent incursions by Russian drones into NATO territory via Ukraine have illustrated the need for a shield against such intrusions – preferably located already within Ukraine rather than in NATO’s eastern flank countries such as Poland, Slovakia, Hungary and Romania.
Third, politicians, diplomats, journalists, development workers and other citizens of the CoW states regularly travel to Ukraine vial rail- and highways that need to be protected from Russian unmanned aerial vehicles during these trips. Fourth, through its Black Sea ports, Ukraine exports, among other things, grain and other agricultural products that are important for global food price stability, which is in the vital collective interest of humankind – including the countries of the CoW. Fifth, Ukrainian gas storage facilities contain natural gas from CoW countries that is their property and also need to be protected. Last but not least, shielding Ukraine’s nuclear power plants from hits by missiles, rockets and drones would be in the interests not only of the eastern EU member states, but also of nearby Russia, Belarus and Moldova.
Conclusions and Policy Recommendations
Unequivocal, clearly defined security guarantees are not the only precondition for, but nonetheless central to, the functioning of a future ceasefire. However, the term should be carefully used to avoid raising expectations that cannot be fulfilled, or to falsely suggest qualitatively different Western engagement in Ukraine once the fighting ends. In particular, it is not certain that European or other countries will send ground troops and warships to secure a future ceasefire. Nor is the role the United States would eventually be ready to play in such a deployment clear.
In future, circumstances might change and foreign ground troops in Ukraine as well as maritime engagement in the Black Sea might become less problematic and more useful instruments. For instance, UN peacekeepers could be deployed to co-guard a fully restored Russo-Ukrainian border. A reassurance force could be sent to Ukraine once it has become a NATO member. Under today’s conditions, however, debates about a peacekeeping operation or reassurance force in Ukraine are a distraction from more salient topics. They divert attention from the military support required for Kyiv today, and from more productive paths to guaranteeing Ukrainian security when high-intensity fighting ends.
The primary source of security for Ukraine is and will continue to be its own armed forces – regardless of whether the war continues or ends soon. The most obvious way to increase Ukrainian security both before and after a ceasefire will be to intensify and expand military-industrial collaboration and other resilience-related cooperation between Ukraine and the CoW. In addition, a geographically limited deployment of European air forces over and in western and central Ukraine to intercept missiles and drones is already possible today. In addition, the placement of CoW liaison officers and joint Ukrainian-CoW exercises and training in Ukraine are both possible and necessary before and after a truce.
Sustaining or even expanding current support for Ukraine with weapon deliveries, joint ventures, intelligence exchange and combat training under conditions of a ceasefire might to some diplomats and politicians appear counterintuitive, unnecessary, or even provocative. However, the viciousness of Russian Ukrainophobia – as demonstrated by Moscow’s ruthless behaviour in Ukraine since 2022 – is and presumably will remain high. Moscow’s aggression can only be constrained by a Ukraine armed to its teeth – a condition that applies to both war and peace time.
The provision of security guarantees for Ukraine by CoW countries will largely mean continuation or extension of current military assistance to Kyiv through weapon deliveries, investment in the Ukrainian military-industrial complex, intelligence sharing, combat training, technical cooperation and financial help. CoW countries should provide such support Ukraine before and after achievement of a ceasefire. Those countries that currently assist Ukraine and will provide security guarantees should transform their wartime aid into peacetime military support for Ukraine, and can justify such a redesignation as designed to deter Russia from re-escalation.
The central concluding advice for diplomats, politicians, journalists and other commentators that emerges from the above and similar reports is, when contributing to the discussion or design of security guarantees, to focus on those instruments that can be realistically and rapidly applied once a ceasefire begins. Moreover, the discussion and planning of post-war security guarantees should not distract from the more important task of creating the conditions that can end high-intensity fighting in the first place, and enable the start of an at least partial truce. Many of the instruments that today can serve to end the war will be the same as those that will help to preserve a future peace.
[1] Yet another use of the concept of “security guarantees” not discussed here but currently becoming salient in Ukrainian and western debates about Russia’s confrontation with the West has a completely different direction. Various European analysts have started to discuss the provision of Ukrainian security guarantees for certain NATO and EU countries. In particular, Estonia, Latvia and Lithuania could become targets of Russia’s expansionism once a ceasefire in Ukraine begins, and hundreds of thousands of Russian troops become available for Moscow’s operations elsewhere. In such a scenario, the technologically advanced and battle-hardened Ukrainian armed forces could become a valuable partner for the armies of the three Baltic states. Kyiv might be able to make a more important contribution to their security than most NATO partners of Tallinn, Riga and Vilnius.
[2] The CoW is an informal ad hoc alliance of 33 pro-Ukrainian European, American, Asian and Oceanic countries. These nations have gradually assembled since the spring of 2025, and agree to provide, in one way or another, support for Ukraine, including assuring a ceasefire once it is achieved.
