U.S. Secretary of State John Kerry says that the Untied States will act as guarantor of peace in Ukraine, which is realistic if Russia and separatists in Donbas fulfill undertaken commitments.

"I guarantee that the United States will act as guarantor of the peace settlement if it could be reached," Kerry said at a joint briefing with Ukrainian Prime Minister Arseniy Yatseniuk in Kyiv on Thursday.

"Neither the United States nor Ukraine, or our European partners want this conflict with Russia to go on. All we're asking is that Russia and separatists uphold and respect the commitments they've undertaken, and observe a real ceasefire, including the withdrawal of weapons and equipment, pull out foreign troops from the territory of Ukraine, release hostages and respect the borders of Ukraine and its sovereignty," he said.

Ukraine in turn undertook commitments in respect of Donbas' special status to give more freedom to municipalities in the region, he said.

"This remains in force, both commitments to conduct constitutional reform and commitments to hold a free election in Donbas," he said.

""We obviously are prepared to negotiate the respect for the international border, negotiate the return of hostages, negotiate the line of control, negotiate the political process going forward that can guarantee to those who call themselves separatists, though they're not really separating from Ukraine. They want to be part of Ukraine, they want greater rights. And the Government of Ukraine has made it clear to them they can have greater rights," he said.

Speaking about relations with Russia, Kerry said that there is still a way back to better ties with Europe, with the West, with the United States.

"There is a way to get back to a cooperative set of measures that we could take together. But it begins with a ceasefire and with allowing Russia – allowing Ukraine to control its own international border and respect that border and begin to move the heavy machinery, the heavy weapons of war, out to the opposite side of that border," Kerry said.