The idea that European governments could dispatch forces to Ukraine to help guarantee any future peace agreement with Russia raises multiple questions, most of them unresolved.
How many troops? From what countries? To do what? With what US support, if any?
Here is a summary of what has emerged so far.
- WHAT COUNTRIES? -
Two countries, Britain and France, stand out for now.
UK Prime minister Keir Starmer has said he was willing to put "our own troops on the ground if necessary", but added that a US security guarantee would be the "only way" to prevent Russia from attacking Ukraine again.
France -- which already stunned allies a year ago with a proposal to deploy western troops in Ukraine -- still appears open to doing so in the future.
Europeans elsewhere are more cautious, including governments that have pursued a hard line towards Vladimir Putin's Russia.
Poland, which is preparing for a presidential election in May, said it won't participate because as a frontline state, its army is needed to defend its own territory.
Sweden has ruled nothing out, while the Baltic countries worry that a Western force in Ukraine could deplete NATO troops currently stationed on their territory.
Germany's future chancellor Friedrich Merz says it's too early to discuss the topic, Italy has been unenthusiastic and Hungary appears dead against.
- UNDER WHAT CONDITIONS? -
Faced with a public that is worried about sending soldiers into danger, European leaders stress that they would dispatch only non-combat units to Ukraine.
"France is not about to send belligerent ground troops into a conflict, to the frontline," said French President Emmanuel Macron.
But uncertainty reigns, especially on the timing of any troop dispatch. Would it come after a ceasefire, or only once a proper peace agreement is signed?
But the most crucial unknown of all concerns American support, or lack thereof.
Starmer's wish list as he prepares for talks in Washington Thursday is topped by the hope to secure assurances from President Donald Trump that the United States will provide a so-called backstop, possibly in the form of air cover, intelligence and logistics, to support any European troops sent to Ukraine.
Macron, meanwhile, has already asked Trump for "American support" and claimed to have made some headway, but Trump himself has been evasive, or even silent, on the question.
"Basically what all the Europeans are saying is that we can't do this without an American backstop," said one European source.
The United States has already ruled out sending ground troops to Ukraine.
- TO DO WHAT, EXACTLY? -
Options on the table range from deploying monitors of a ceasefire -- by definition close to the 1,000-kilometre (620-mile) frontline between Russian and Ukrainian forces -- to a "reassurance" force, similar to the multinational presence that NATO keeps on its eastern flank.
France and Britain have begun thinking about the possible creation of a European force tasked with preventing Russian attacks on Ukrainian cities, infrastructure and ports following any ceasefire, according to British media.
But the idea, said a French source close to the talks, would be to deploy troops behind current lines, "not on the frontline facing the Russians".
Another option could be to train Ukrainian troops in the west of the country, according to a European source.
Ukrainian President Volodymyr Zelensky told a conference in Munich this month that it was up to Ukraine to secure its borders but that he needed "1.3 to 1.5 million soldiers" to make his army "comparable" to that of Russia.
Ukraine currently has 800,000 military personnel.
- HOW MANY SOLDIERS? -
The amount of troops sent will depend on the choice of mission.
Zelensky said in January that 200,000 would be the "minimum", corresponding to the size of an army NATO -- including US troops -- would be expected to mobilise in the first 30 days of any major conflict.
Without US participation, Europeans alone have no hope of getting even close.
"The most we could do is 40,000 to 50,000," said Michel Goya, a historian and former soldier.
Paris and London seem to have a contingent of fewer than 30,000 in mind, according to British media.
- WHAT ABOUT TRUMP AND PUTIN? -
Putin said this week there was "nothing wrong" with European countries taking part in efforts to end the fighting in Ukraine, but Moscow has in the past voiced its opposition to any European troop deployments in Ukraine.
Trump, meanwhile, has declared himself to be "all for" European peacekeeping troops in Ukraine, and said he expected Putin would be, too.
