Talks aimed at ensuring a stable cease-fire between Ukrainian government forces and pro-Russian separatists have ended after more than five hours.
There was no indication of progress or when the next round might take place.
The peace talks in the Belarusian capital, Minsk, brought together representatives of Ukraine, Russia, the rebels, and the Organization for Security and Cooperation in Europe (OSCE).
A second round had been tentatively set for December 26, but the Belarusian Foreign Ministry said that it was unclear if that would take place.
"We had a difficult preliminary meeting," separatist mediator Denis Pushilin told a separatist news site. "The date and time of the next meeting is still up in the air. It is under discussion."
Aleksandr Zakharchenko, a rebel leader in the self-proclaimed Donetsk People's Republic, said vaguely that "a second round is still ahead."
Heidi Tagliavini, the OSCE's lead figure since the peace talks began, said the participants would discuss on December 24 a pullback of heavy weaponry, a complete exchange of war prisoners, and the delivery of humanitarian aid to the region.
Last month, Kyiv suspended social services to the population of the rebel-held parts of eastern Ukraine.
The Ukrainian president’s top foreign policy adviser, Valeriy Chaly, has said the very fact that the sides had managed to arrange such a meeting was a promising sign.
"The work begins today, and by some point around Friday [December 26] we should be able to achieve concrete results," Chaly told reporters in Kyiv.
And Russia's Deputy Foreign Minister Konstantin Dolgov said the consultations presented a "real chance" for peace.
But there are sharply contrasting views between the negotiating parties about Ukraine’s future place in Europe and its system of government.
Those divisions could block a solution to the conflict which has claimed the lives of more than 4,700 people since April.
The United Nations says more than 1,300 people have been killed there since talks in Minsk produced an often violated cease-fire agreement on September 5.
Separatist leaders in Ukraine’s eastern regions of Luhansk and Donetsk have declared their own republics and have said they will settle for no less than Ukraine becoming a loose federation in which they manage most of their own affairs.
Those separatist calls are backed firmly by Russia but have been rejected by Ukrainian nationalists who comprise an important part of Ukrainian President Petro Poroshenko’s government.
The negotiations also could be complicated further by a vote from Ukraine’s parliament on December 23 to abandon the country's neutral "non-bloc" status and set a course for NATO membership.
On December 24, Russian Deputy Defense Minister Anatoly Antonov said that unidentified NATO members had pushed Ukraine to make the move in a bid to turn it into a "forward line for confronting Russia."
But Valeriy Chalyi emphasized that the parliament vote doesn't mean that the bid to join the alliance is on the immediate agenda.
Meanwhile, tensions over Crimea, which was annexed by Russia in March, persisted when electricity supplies to the peninsula were cut for several hours in the afternoon.
Ukrainian Energy Minister Vladimir Demchishin said the cutoff was due to Crimea exceeding limits on its power demands.
Crimea relies on mainland Ukraine for some 80 percent of its power.
With reporting by Reuters, AP, AFP, dpa, and Interfax