Faced with demands from the United States to provide military forces to implement a future peace agreement in Ukraine, Europe finds itself in a dilemma.
Experts say that sending a European peacekeeping force to Ukraine could strain and weaken NATO's own defenses, and that the mission would still require US support to be successful.
While US troops on the ground may not be necessary, deterrence in the form of US intermediate-range missiles and, ultimately, nuclear weapons will remain crucial, writes Reuters.
"I'm not sure any security guarantee will be 100 percent credible against an aggressive and nationalist Putin (Russian President Vladimir) if it doesn't involve Americans in some way," said Mark Lyall Grant, Britain's national security adviser during part of Donald Trump's first term.
European officials also argue that only a US guarantee would protect European peacekeepers and deter Russia from any future attack on Ukraine.
US President Donald Trump shocked Europeans last week by organizing bilateral peace talks with Russia, which were launched yesterday in Riyadh, while Defense Secretary Pete Hegseth told allies that "any security guarantee must be backed by capable European and non-European troops."
He made it clear that American troops would not be sent to Ukraine.
Experts warn that the deployment of large European forces in Ukraine could weaken NATO's defenses against a broader and growing threat from Russia.
At an emergency meeting in Paris on Monday, European leaders remained divided over the idea of sending peacekeepers to Ukraine - a plan that some European countries began discussing last year at the initiative of France.
Reuters writes that such a mission would increase the risk of direct confrontation with Russia and further strain European militaries, whose weapons stocks have been depleted by donations to Ukraine and which rely heavily on US support for major military operations.
British Prime Minister Keir Starmer said on Monday that he was ready to send troops to Ukraine, but that there would also have to be American security support.
Experts warn that the deployment of large European forces in Ukraine could weaken NATO's defenses against a broader and growing threat from Russia, as an end to the conflict would allow Russia's war economy to quickly rebuild its military stockpiles.
Some also doubt that European countries, already struggling to improve their combat readiness after decades of relative peace since the end of the Cold War, could quickly mobilize sufficient numbers of combat-ready troops - especially if they were tasked with securing the more than 2.000 km line of contact with Russia and its ally Belarus.
Peacekeeping mission in Kosovo begins with 48.000 troops
Claudia Major, an analyst at the German SWP Institute, said it was almost impossible for Europe to assemble such a peacekeeping force on its own.
Estimates of its required size range from 40.000 to 150.000 troops, in addition to Ukrainian forces, she told Germany's ARD on Monday.
Reuters writes that NATO's peacekeeping mission in Kosovo began with 48.000 troops in 1999, securing a territory of 11.000 square kilometers, while Ukraine is almost 55 times larger.
“Europe doesn’t have that much military strength right now unless it weakens its defenses or its planned defense of the Baltics, which is obviously controversial,” Major said.
"At the same time, they lack key capabilities in the areas of reconnaissance, air defense, and targeting, which only the US has in sufficient quantities."
Michael Coffman, a senior fellow at the Carnegie Endowment, said that deploying three brigades, units of about 3.000 to 5.000 soldiers, could be enough to secure four to five sectors of the front where the fighting is most intense.
Normal rotations for rest and training would triple the number of troops needed to perhaps 50.000, “without eliminating all existing regional defense plans,” he posted on the X platform.
"But these forces would have to have battalions close to the front, not aimlessly spending time in western Ukraine training," he warned, adding that these units would have to be mobile.
“More importantly, what should these forces do and how would they act as a deterrent?”
He also asked what military actions would be taken in the event that Russia violates the ceasefire: "If that is a red line, what kind of reaction does it provoke?"
Some experts advocate leaving the security of the contact line to Ukrainian forces, while deterrents would remain outside Ukraine.
Hegseth did not explicitly state that peacekeepers must be stationed inside Ukraine, but he made it clear that they would not be covered by NATO's mutual defense clause, Article 5.
However, Russian Foreign Minister Sergei Lavrov said yesterday in Riyadh that the presence of any troops from NATO countries inside Ukraine is unacceptable for Russia, regardless of under which flag they would be deployed.
But, as the Reuters analysis points out, providing a deterrent outside Ukrainian territory could pose a different dilemma for the Europeans, who lack medium-range weapons with which to strike Russian targets from a distance in retaliation for ceasefire violations.
They also lack the vast American nuclear arsenal that provides the ultimate deterrent against a nuclear-armed Russia.
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