KIEV, July 24 - The leaders of France, Germany, Russia and Ukraine have vowed to go ahead with a peace plan for eastern Ukraine, The Associated Press reported.

France, Germany and Russia have mediated talks between the Ukrainian government and Russia-backed rebels who have been fighting since April 2014 in a conflict that has killed more than 10,000 people.

President Petro Poroshenko's office said that French President Emmanuel Macron, German Chancellor Angela Merkel and Russian President Vladimir Putin held a phone call Monday and vowed to help implement the peace deal they had brokered.

The separatists last week proclaimed a new state that aspires to include not only the areas in eastern Ukraine that they now control but territory beyond that. Poroshenko's office said both Macron and Merkel vehemently rejected the idea of the rebel state.

Kurt Volker, a former U.S. ambassador to NATO, who the U.S. special envoy to the Ukraine peace talks on July 7, said Sunday Russian aggression is to blame for violence in eastern Ukraine, where people are dying in what should be seen as a "hot war" rather than a "frozen conflict.”

On a visit to the Ukrainian-held town of Kramatorsk, 690 km (430 miles) southeast of Kiev, Volker said he would prepare a set of recommendations on how Washington can better engage with the peace process.

"This is not a frozen conflict, this is a hot war, and it's an immediate crisis that we all need to address as quickly as possible," he said.

Relations between Ukraine and Russia went into freefall after Moscow's 2014 annexation of Crimea and the subsequent outbreak of a pro-Russian insurgency in the eastern Donbass region.

Ukraine accuses Russian of sending in its own soldiers and military equipment, which Moscow denies.

Volker replied in the affirmative when asked whether he saw the conflict as being as the result of Russian aggression rather than internal Ukrainian factors.

"We've seen what's happened, we understand the way this conflict has begun, we understand the way it is being managed today, and that's why it's important that the United States become more engaged." (ap/nr/ez)