A tense summit in Minsk between the leaders of Ukraine, Russia, Germany and France dragged on through the night and into the morning of February 12 as they wrangled over a plan to end 10 months of fighting in eastern Ukraine.
The meeting in the Belarusian capital is being attended by Russian President Vladimir Putin, his Ukrainian counterpart Petro Poroshenko, German Chancellor Angela Merkel, and French President Francois Hollande.
By 0800 local time (0600 Prague time) the talks held at the opulent presidential palace in Minsk had gone beyond the 12-hour mark.
An unnamed source told western media that there was "hope" an agreement would be signed soon.
Reuters quoted an unnamed diplomatic source as saying the four leaders will sign a document on solving the conflict. The source would not provide details of the nature of the document.
TASS reported that the document covers 12 or 13 points.
Before the four-way talks began, Poroshenko was quoted as saying they were the last chance to end the conflict.
According to the Interfax news agency, he said: "Either there is deescalation, a cease-fire, and a withdrawal of heavy weapons, or the situation gets out of control."
The four leaders held a number of rounds of closed-door talks, first among themselves, then with their foreign ministers and top aides, and then again without aides.
The German Foreign Ministry said that the talks are "not easy and continuing," adding that minister Frank-Walter Steinmeier is delaying his departure for a planned trip to Brazil.
By contrast, Russian Foreign Minister Sergei Lavrov said earlier that the talks were going "better than super."
Ukrainian presidential aide Valeriy Chaly said in a Facebook post early on February 12 that the talks could continue for at least another five to six hours.
Chaly said, "we should not leave here without an agreement on an unconditional cease-fire. There's a battle of nerves under way."
Earlier, a senior Ukrainian diplomatic source told French news agency AFP that the talks were making "progress" but also proving "very hard."
Another source close to the discussions had said the leaders hoped to sign a joint statement calling for the fulfilment of an earlier failed peace plan signed by Kyiv and the rebels in September, also in Minsk.
The September deal has been shattered by daily fighting, and hundreds of combatants and civilians have been killed in the past four weeks in an upsurge of hostilities that the United States says is the result of a "Russian-backed offensive."
At the start of the talks, television footage from the venue showed a grim-looking Poroshenko shaking hands briefly with Putin at the start of the talks.
Prospects for a breakthrough at the meeting were clouded by continued fighting and conflicting interests in a war that has killed more than 5,350 people since April and sparked the tensest standoff between Moscow and the West since the Cold War.
However, hopes for a deal were raised by the news that the top separatist leaders, Aleksandr Zakharchenko and Igor Plotnitsky, arrived February 11 in Minsk. Andrei Purgin of the self-declared Donetsk People's Republic told German news agency dpa that the two will sign an agreement if the talks are successful.
The meeting is part of a diplomatic push initiated by Merkel and French President Francois Hollande, who took new proposals to Kyiv and Minsk last week in a desperate effort to find a solution to the conflict between Ukrainian government forces and Russian-backed separatists.
A Ukrainian delegation source told Reuters that the four leaders are planning to sign a joint declaration supporting Ukraine's territorial integrity and sovereignty.
The source said a separate document would be prepared by the three-way Contact Group comprising Russia, Ukraine and the Organization for Security and Cooperation in Europe (OSCE) affirming commitment to the September cease-fire agreement.
Western diplomats warn that the sides remain deadlocked over key issues and Poroshenko said before the talks he could introduce martial law throughout the country if the Minsk talks fail to stop the war.
Meanwhile, news reports said at least two people were killed in two separate incidents on February 11 in Donetsk, one of two rebel-held strongholds in eastern Ukraine.
Pro-Russian authorities said at least one person was reported killed when an artillery shell hit a hospital in the city in the evening.
Earlier, witnesses said at least one person was killed when a shell hit a bus station in the center of the city.The rebels put the death toll in that incident at five.
Ukrainian military spokesman Vladyslav Seleznyov told a briefing on February 11 that 17 armed forces servicemen and two Interior Ministry troops had been killed in shelling, rocket attacks, and clashes with rebel forces near Debaltseve, a government-held pocket astride a junction between Donetsk and Luhansk.
He said 78 others had been wounded.
Rebels have been trying to drive government troops from Debaltseve for at least a month in an effort to gain more ground, and on February 10 they said they had completely encircled the town.
U.S. President Barack Obama spoke separately by telephone with Putin and Poroshenko on February 10.
The White House said that in the call to Putin, Obama reiterated U.S. support for Ukraine's sovereignty, emphasized the importance of reaching a diplomatic resolution, and urged the Russian president to seize the opportunity for the Minsk talks to bring an end to the conflict.
"However, if Russia continues its aggressive actions in Ukraine, including by sending troops, weapons, and financing to support the separatists, the costs for Russia will rise," the White House said in a statement.
Russia denies sending troops or weapons to Ukraine despite what Kyiv and the West say is incontrovertible evidence of its direct military involvement.
The conflict erupted after Russia seized control over Ukraine's Black Sea peninsula of Crimea in March, following the flight of a Moscow-backed Ukrainian president from Kyiv after months of protests over his decision to scrap plans to sign a landmark agreement with the European Union.
Kyiv and Western governments believe Russia wants to weaken Ukraine and keep it out of NATO by maintaining a "frozen conflict" in the east for years to come, and fear Putin could potentially support a rebel push to seize a swath of territory stretching from Donetsk to Crimea.