Talks in Minsk between the leaders of Ukraine, Russia, Germany and France dragged past dawn as they tussled over a plan to end 10 months of fighting in Ukraine.
A diplomatic source of Reuters news agency said early on Thursday that the leaders of Ukraine, Russia, Germany and France would sign a document after the talks.
The source would not provide details of the nature of the document, Reuters reported.
Tense negotiations dragged on all night after opening on Wednesday evening with a handshake between Ukrainian President Petro Poroshenko and Russian leader Vladimir Putin, who were meeting for the first time since October.
The meeting with German Chancellor Angela Merkel and French President Francois Hollande in the Belarusian capital was part of a diplomatic drive aimed at stopping the crisis.
"Today the peace process for Ukraine is all about Minsk and I hope that the meeting will fulfil our best expectations," Poroshenko told host Belarusian leader Alexander Lukashenko ahead of the talks.
Poroshenko warned before the talks that he would introduce martial law throughout the country if they fail to stop a war that has already claimed more than 5,300 lives.
Martial law would mark a significant escalation of the crisis, freeing up military resources for the fight in the east but also likely leading to the severance of foreign investment for cash-strapped Ukraine.
Poroshenko is scheduled to brief a European Union summit in Brussels on Thursday.
If the Minsk talks fail, US President Barack Obama has warned that Washington may decide to start providing lethal weapons to Ukraine, a step many European leaders oppose for fear of getting drawn into open conflict with Russia.
Separatist negotiators meanwhile met on Wednesday elsewhere in Minsk to agree how to implement previous truce deals with representatives from Kiev, Moscow and mediators from the Organization for Security and Co-operation in Europe.
The most pressing element is the need to agree on an immediate ceasefire between the two sides that would see an end to the surge in fighting that has killed hundreds of civilians in recent weeks.
A key sticking point is whether a new deal will extend rebel control over 500sq km (200 square miles) of territory taken over the past month.
Moscow is also pushing for the separatist-held territories to be granted a large degree of autonomy, but Kiev only says that it is willing to decentralise some powers.
The bloodletting in eastern Ukraine has been relentless in recent weeks as the rebels have pushed deeper into government-held territory and Kiev forces have counter-attacked.
Separatists have been battling for weeks to take the rail hub of Debaltseve, while Ukrainian forces on Tuesday captured ground around the port city of Mariupol.