ANTALYA, TURKEY - US Secretary of State John Kerry on Wednesday warned Russia that now was a critical time to implement a fragile peace deal to end the fighting in Ukraine, after his talks with President Vladimir Putin raised hopes of a slackening in tensions.

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 United States 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 conflict... to 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.

NATO Secretary General Jens Stoltenberg also warned Russia that it has to immediately halt its support of the separatists and withdraw heavy weaponry from the conflict zone. “Actions speak louder than words,” said Stoltenberg.

“Now is the time to act... there is urgency when it comes to fulfilling the Minsk agreement,” he said.

The NATO ministers are meeting for two days in the Turkish resort city, the first time since 2011 that such a meeting is being held outside Brussels.

However, Kerry is leaving early to attend a summit of Gulf leaders hosted by President Barack Obama.

The West accuses Russia of arming separatists in eastern Ukraine and even sending its own troops across the border. Russia denies the charges.

Stoltenberg said that the Antalya talks would be focusing chiefly on the challenge to the alliance to the south from Islamist militants and to the east from Russia.

“To the east, we face a more assertive Russia, responsible for aggressive actions in Ukraine,” he said.

Hosting the NATO ministers, Turkish Prime Minister Ahmet Davutoglu sharply criticised Russia’s behaviour in Ukraine, in unusually sharp comments as his country still maintains warm ties with Moscow. “We should not forget the suffering of the Ukrainian people,” Davutoglu said.

Davutoglu said Russia’s 2014 annexation of Crimea from Ukraine “cannot be accepted in any way” and it was “crucial” to prevent the isolation of the Turkic-speaking Crimean Tatars on the peninsula.