Russia and Ukraine said they had failed to reach any breakthrough in a day of talks with French and German officials aimed at ending an eight-year separatist conflict in eastern Ukraine.
The lack of progress marked a setback for efforts to defuse the wider Ukraine crisis in which Russia has massed more than 100,000 soldiers near Ukraine's borders, raising fears of a war.
Russian envoy Dmitry Kozak told a late-night briefing after Thursday's talks in Berlin that it had not been possible to reconcile Russia and Ukraine's different interpretations of a 2015 agreement aimed at ending fighting between pro-Russian separatists and Ukrainian government forces.
"We did not manage to overcome this," he said.
Ukraine's envoy Andriy Yermak said there had been no breakthrough but both sides agreed to keep talking.
"I hope that we will meet again very soon and continue these negotiations. Everyone is determined to achieve a result," he said.
The conflict in the breakaway Donetsk and Luhansk regions, known together as the Donbass, simmers on despite a notional ceasefire. Observers from the Organisation for Security and Cooperation in Europe (OSCE) record frequent violations, sometimes running into hundreds of incidents daily.
Ukraine says some 15,000 people have been killed since 2014.
Representatives of Russia, Ukraine, the OSCE and the two separatist regions signed a 13-point agreement in February 2015 in Minsk, that was also backed by the leaders of France and Germany.
Russian Foreign Minister Sergei Lavrov accused Ukraine on Thursday of trying to rewrite the agreement and cherry-pick only the elements most advantageous to it.
Ukraine says it is committed to the accord.
"The Ukrainian side is set on constructive dialogue. Everyone confirmed today that we have the Minsk agreements and they need to be fulfilled," Yermak said.
Ukraine rejects Moscow's assertion that it has nothing to do with the conflict, saying Russia has forces inside Ukraine fighting alongside the separatists.
Kyiv refuses to negotiate with the heads of the breakaway regions but President Volodymyr Zelenskiy has proposed direct talks with Russian President Vladimir Putin, which the Kremlin has so far rejected.
Russia denies planning to invade Ukraine but says it wants to enforce "red lines" to make sure that its former Soviet neighbour does not join NATO and that the alliance does not set up bases and missiles there.
(Reporting by Andrey Ostroukh, Natalia Zinets and Matthias Williams; Writing by Mark Trevelyan; Editing by Stephen Coates)
