Leaders of Russia, Ukraine, France and Germany are struggling to reach a deal this morning in marathon talks aimed at ending fighting in eastern Ukraine.
The leaders briefly left the session hall this morning after discussions went through the night, but later came back to continue negotiations.
Speaking to reporters during the break, Ukraine's President Petro Poroshenko said that Russian conditions "are unacceptable".
Ukrainian officials in Kiev said a deal under preparation envisages a ceasefire starting from Saturday and the creation of a buffer zone, but gave no further details.
Parallel to the summit in Minsk, rebel leaders were meeting representatives of Russia, Ukraine and the Organisation for Security and Cooperation in Europe.
Rossiya 24 television and the Tass news agency said the rebel chiefs had refused to endorse a draft document agreed by the four leaders.
More than 5,300 people have died since April in fighting between Ukrainian forces and Russia-backed separatists in two eastern provinces and the bloodshed has risen sharply in recent weeks.
Despite the continuing talks, rebels and government troops reported fighting across eastern Ukraine.
As President Barack Obama considers rising calls at home for sending US lethal aid to Ukraine, European leaders fear that would only aggravate the fight.
Russia, meanwhile, faces a severe economic downturn driven in part by sanctions the West has imposed for supporting the separatists with troops and equipment, which Moscow denies.
The urgency felt by all sides appeared to be underlined by the length and discomfort of the talks among German Chancellor Angela Merkel, French President Francois Hollande, Ukrainian President Petro Poroshenko and Russian President Vladimir Putin.
They sat down yesterday evening in the Belarusian capital and the talks continued through the night as crowds of reporters waited anxiously in a marble-floored, chandeliered convention hall.
The French-German diplomatic blitz began last week when Ms Merkel and Mr Hollande visited Kiev and Moscow.
“The entire world is waiting to see whether the situation moves toward de-escalation, weapons pullback, ceasefire, or ... spins out of control,” Mr Poroshenko said yesterday before sitting down for talks.
Russian foreign minister Sergey Lavrov signalled some progress, saying just before midnight that the talks were “active, better than super”.
But it was unclear when a decision might be announced – and how soon the shooting would stop if an agreement is reached.
A top rebel official, Andrei Purgin, told Russian television that it might take a day or more for hostilities to end even if a ceasefire is called.