Earlier, four European sources said the U.S. had sent a document asking questions that included possible future troop contributions, with two of the sources adding that it had been sent earlier this week.

"The Americans have provided Europeans with the questionnaire on what would be possible," Finnish President Alexander Stubb told Reuters at the Munich Security Conference.

"This will force Europeans to think, then it's up to the Europeans to decide whether they actually answer the questionnaire, or whether they answer it together."

The Financial Times first reported that Washington had asked its European allies to provide information on weaponry, peacekeeping troops and security arrangements they could provide for Ukraine.

"The idea is evidently to see how European allies see the possible framework for negotiations to put an end to the conflict, and the possible engagement of Europe and the United States," said a European diplomat aware of the document.

It included six questions with one specifically for member states of the European Union, one diplomat said.

Ukrainian President Volodymyr Zelenskiy called on Saturday for the creation of a European army, arguing the continent could no longer be sure of protection from the United States and would only get respect from Washington with a strong military.

U.S. President Donald Trump spoke last week with Russian President Vladimir Putin, saying that negotiations to end the war should begin now.

The prospect of a rapid settlement has focused minds in Kyiv and Europe on the urgent need for security guarantees and on what role Europe may have to play should the United States row back on its support to Ukraine and the continent as a whole.

"The Americans are approaching European capitals and asking how many soldiers they are ready to deploy," a third diplomat said.

The U.S. State Department did not immediately respond to a request for comment.