The U.S. and Russia said they'll work together to shore up a Ukrainian peace deal that's come under increasing strain amid violations of a cease-fire in effect since February.

Russian Foreign Minister Sergei Lavrov said after meeting with U.S. Secretary of State John Kerry that, while differences exist between Russia and the U.S. over Ukraine, the two countries believe it's essential to resolve the yearlong conflict peacefully. Kerry spent four hours with President Vladimir Putin in the Black Sea resort of Sochi, their first meeting in two years, and more than four hours with Lavrov.

"We have agreed to use the influence of the United States and the Russian Federation on the parties to the conflict in order to consistently strongly encourage them to seek agreement on the practical implementation of everything that was agreed upon," Lavrov said Tuesday.

The U.S., which has been accused by Russia of encouraging Ukraine to sabotage the peace process, wasn't part of the European-mediated negotiations that led to the accord in Minsk. More than 6,100 people have died and a million people have fled their homes in fighting between Ukrainian government forces and separatists that has sparked the biggest geopolitical confrontation since the Cold War.

Kerry said the U.S. had expressed its "deep concern" at Russia's continued military support for pro-Russian rebels. At the same time, he said that Russia and the U.S. shared the view that implementing the peace is the only way forward.