BÉNOUVILLE, France — As President Obama wrapped up a four-day European trip on Friday, the violent conflict over Ukraine seemed to move toward a new phase of diplomacy, but it remained unclear whether the Russian president, Vladimir V. Putin, was genuinely willing or able to call off a pro-Russian uprising across his border.

Mr. Putin used a trip to France commemorating the 70th anniversary of D-Day to meet for the first time with his newly elected counterpart in Ukraine, Petro O. Poroshenko, and the two discussed the possibility of a cease-fire in the eastern part of the country. After a ceremonial luncheon in a chateau here, Mr. Putin also held an unscheduled conversation with Mr. Obama in addition to more formal meetings with the leaders of Britain, France and Germany.

The blitz of diplomacy may presage a new stage in the crisis, and Mr. Obama left France on Friday evening more optimistic than when he arrived. Mr. Obama used the trip to shore up solidarity with European allies, and American officials said they hoped that despite differences of approach, there was enough resolve to persuade Mr. Putin to change course. They said they wanted to give him a way out of the clash.