A top UN official said the negotiations aimed at implementing the 2015 Minsk accords and ending the conflict in eastern Ukraine have lost momentum.
Assistant Secretary-General Miroslav Jenca made the comment in a speech before the UN Security Council on February 12, at an event marking the fourth anniversary of the accords.
Jenca said negotiations "appear to have lost momentum" and that neither Russia nor Ukraine appear to be willing to agree on key steps forward.
The conflict, which erupted in 2014 at around the same time that Russia annexed Ukraine's Crimea Peninsula, has killed more than 10,000 people and displaced more than 1 million.
The fighting pits Ukrainian government troops and allied militias against fighters that Western officials say have been funded and equipped by Russian military units.
Signed roughly a year after full-scale fighting erupted, the Minsk accords laid out a blueprint of political steps, including elections, that would end the conflict.
Both Russia and Ukraine have blamed each other for the failure to implement the agreement.
The United States was not directly involved in the Minsk negotiations but has had a special envoy dedicated to resolving the fighting. That envoy, Kurt Volker, said in a post on Twitter that Russia continued to violate the agreement.
"In the four years since [Minsk], Russia has continued to violate the Minsk agreements every day. It's time for Peace for Ukraine," he wrote.
Russia's UN envoy, meanwhile, accused the West of using Ukraine as a pawn in a geopolitical chess game.
"Unfortunately, it is obvious to us that the West is not interested in Ukraine itself, in its fate and well-being of its citizens," Vasily Nebenzya was quoted by the state news agency TASS as saying. "For them, this country is a mere pawn in the geopolitical confrontation with Russia."
The five current European Union members on the Security Council issued a joint statement accusing Russia of continuing to fuel the conflict.
"We call on Russia to immediately stop fueling the conflict by providing financial and military support to armed foundations," the statement said.