Talks aimed at reaching a stable ceasefire in Ukraine between its government forces and pro-Russian armed groups ended after more than five hours.
There was no indication of progress, and questions about when the next round might take place.
The opening session occurred in the Belarusian capital Minsk, a day after Ukraine's decision to drop its non-aligned status, which added a new element of tension to the attempts to resolve the violent crisis in the country.
The talks were to discuss how to improve an often-violated ceasefire that was declared in September, to pull back heavy weapons and to exchange of war prisoners.
The negotiators included representatives of Ukraine, Russia, pro-Russia rebels and the Organisation for Security and Co-operation in Europe.
News media were not allowed access to the meeting and the participants left the session without comment.
Another round had been tentatively set for tomorrow, but the Belarusian foreign ministry said after the session's conclusion that it was unclear if that would take place.
Fighting in eastern Ukraine between government forces, volunteer battalions and pro-Russia separatists has claimed more than 4,700 lives since it began this spring.
Previous rounds of talks in September produced a ceasefire and an agreement to pull back heavy weapons, but both sides have failed to agree on a line of division and fighting continued.
Hostilities have diminished in the past month amid renewed peace efforts. But new tensions hover over the renewed talks.
On Tuesday, the Ukrainian parliament voted to abandon the country's non-aligned status, a first step toward a possible bid for Nato membership. Ukraine's joining the Western military alliance would be anathema to Moscow.
The insurgency in the Donetsk and the Luhansk regions of eastern Ukraine erupted in April following Moscow's annexation of Ukraine's Crimean Peninsula, which was partly rooted in Russian fears that Nato could establish bases in the same area that is home to the Russian navy's Black Sea Fleet.
Valeriy Chalyi, a deputy chief of staff of the Ukrainian president, emphasised yesterday that the Ukrainian parliament vote does not mean the bid to join the alliance is on the immediate agenda.
He added that Ukraine should focus on reforms to meet membership criteria.
Despite that, Moscow strongly protested against the Ukrainian move.
Russian deputy defence minister Anatoly Antonov said unidentified Nato members had pushed Ukraine to make the move in a bid to turn it into a "forward line for confronting Russia".
It was not immediately clear if Ukraine's possible Nato aspirations could be used in the Minsk negotiations to pressure Russia, which Kiev and the West allege has backed the eastern insurgency with soldiers, tanks and artillery.
Tensions over Crimea persisted yesterday when Ukraine cut electricity supplies to the peninsula for several hours in the afternoon, then reportedly resumed the cut in the evening. Crimea relies on mainland Ukraine for about 80% of its power.
Ukraine's energy system in turn has been undermined by the fighting in the east, which supplied much of the power system's coal.
Ukrainian energy minister Vladimir Demchishin said the daytime cut-off was due to Crimea exceeding limits on its power demands.
Russia, meanwhile, remains under hard economic pressure partly due to sanctions imposed on it by the West for the Crimea annexation and Moscow's support of the eastern rebels.
With inflation showing clear signs of picking up, Russia's central bank said yesterday it will look to help companies with their foreign debts - a move it hopes will ease the pressure on the national currency, which had lost more than 40% of its value against the dollar this year.