Kerry said there was an "enormous moment of opportunity" to bring to an end over a year of fighting in eastern Ukraine between government forces and pro-Russia separatists which has dragged relations between Moscow and the West to a new post-Cold War low.
Kerry, speaking at the NATO foreign ministers' meeting in the southern Turkish city of Antalya hours after talking with Putin in Russia, said that the alliance was in "unanimity" on the importance of this year's Minsk truce agreement being fulfilled by Moscow.
"I think there was strong agreement among all of the NATO members that this is a critical moment for action by Russia, by the separatists, to live up to the Minsk agreement."
He added that it was also "critical" for observers from the Organization for Security and Cooperation in Europe (OSCE) to be allowed into the conflict areas to monitor the truce.
The intensity of the fighting in eastern Ukraine controlled by pro-Russia separatists has declined since the Minsk deal but deadly clashes remain frequent.
Kerry had met Putin on Tuesday for the highest level US visit to Russia since the Ukraine conflict erupted in 2013, in a possible sign of a cautious thaw between the two sides.The talks lasted for four hours and even though there was no concrete breakthrough, Russian Foreign Minister Sergei Lavrov had said that the talks helped the two sides to "better understand each other".

Kerry said in Antalya the US and its NATO allies would prefer not to keep sanctions in place against Russia but would keep the measures in order to ensure peace in Ukraine.
"This is an enormous moment of opportunity for the find a path of certainty and resolution," said Kerry, who earlier met with Ukrainian Foreign Minister Pavlo Klimkin.
"And we hope very, very much that President Putin, Russia, the separatists, will come together to work with Ukraine in order to fully implement it (Minsk) and make progress," said Kerry.
"Our preference is not to have sanctions, but the sanctions will be there in an effort to try to secure the peace that everybody wants in Ukraine," he added.

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