KYIV/BERLIN/PARIS, May 20 (Reuters) - For Ukraine and its allies, who spent months trying to win Donald Trump over to their cause in the war started by Russia, it is back to square one.

In a two-hour conversation with Russian leader Vladimir Putin late on Monday, the U.S. president dropped his earlier insistence on an unconditional 30-day ceasefire that he hoped would kickstart what promise to be long and tortuous peace talks.