U.S. officials say the coming week will be "very critical" for determining whether it remains involved in talks.

President Trump "wants to see a permanent ceasefire first, to stop the killing, stop the bloodshed," press secretary Karoline Leavitt said.

Russian President Vladimir Putin on Monday declared a unilateral three-day ceasefire in Ukraine next month, a move met with skepticism by Ukrainian officials who demanded the Kremlin leader immediately accept a longer truce proposal from the United States that he has so far rejected.