Minsk talks ended in the late hours of this morning and the leaders of Ukraine, Russia, France and Germany have reportedly agreed on a document that proposes to achieve a ceasefire in eastern Ukraine in 48 hours.
Talks to end the growing carnage in the deadly conflict in east Ukraine began in the Belarusian capital Minsk yesterday after a week of EU shuttle diplomacy.
As the tense negotiations began, Russian president Vladimir Putin shook hands briskly with Ukrainian leader Petro Poroshenko.
Russia has been accused of arming and reinforcing pro-Russian rebels in east Ukraine - a claim it denies.
Brokering the ceasefire bid are German chancellor Angela Merkel and French president Francois Hollande.
The talks are set to focus on securing a ceasefire, withdrawal of heavy weapons and creating a demilitarised zone.
A peace plan is believed to comprise of two parts:
However, fighting claimed more than 20 lives in the hours leading up to the talks. Shelling killed at least five people in the rebel-held city of Donetsk while 19 Ukrainian soldiers died along the front line.
While the Ukrainian government is seeking a demarcation line based on the failed ceasefire agreed on September 5 in Belarus last year, the rebels want a new truce to reflect the gains they have made in recent weeks, the BBC's James Reynolds reports from Donetsk.
More than 5,400 people have died since the conflict began, and there has been a dramatic rise in casualties in recent days, with 263 civilians killed in populated areas between January 31 and February 5.
Even as the talks began, pro-Moscow separatists tightened the pressure on Kiev by launching some of the war's worst fighting.
Rebels who tore up a five-month-old truce in January are trying to encircle government forces in Debaltseve, a strategic location that would let them link up their main strongholds.
The escalating violence, including a rocket attack that killed 17 people in government-held territory on Tuesday, could be intended to force Ukraine to accept a deal recognising the rebel advance.
The summit was being held in neighbouring Belarus under the Franco-German proposal to try to halt the fighting.
Chancellor Merkel and President Hollande began talks with Ukraine's Mr Poroshenko and Russia's Mr Putin.
The leaders were planning to sign a joint declaration supporting Ukraine's territorial integrity and sovereignty, a Ukrainian delegation source said.
The source said a separate document would be prepared by a "contact group" of Russia, Ukraine and the Organisation for Security and Co-operation in Europe affirming commitment to a ceasefire plan drawn up in Minsk last September and also signed by separatist leaders.
The comments were a partial read-out from the Ukrainian side and with the summit starting in earnest it was too early to say what compromise, if any, had been worked out between Ukraine and Russia.
The four leaders met alone at about 5pm and then went into a full summit with their delegations.
Armoured columns of Russian-speaking soldiers with no insignia have been advancing for days around Debaltseve.
Last week they captured the small town of Vuhlehirsk next to Debaltseve, and a reconnaissance unit was there on Tuesday salvaging equipment from abandoned Ukrainian trenches.
The squad's commander said his men did not want a truce while they had government forces on the run.
On the Russian side of the border, Moscow announced war games on Tuesday on the eve of the talks.
The handshake between the Russian and Ukrainian leaders was extremely brief, with Mr Poroshenko coming up to Mr Putin without smiling. There was little warmth in the tense greetings.
Speaking earlier, Mr Poroshenko said the situation threatened to spin "out of control" if the parties did not agree to de-escalation and a ceasefire.
Warning that his government was prepared to impose martial law, he said the Minsk summit was one of the final chances to bring about an unconditional ceasefire and withdrawal of heavy weapons.
Russian Foreign Minister Sergei Lavrov cautioned against making an issue of Ukraine's unguarded eastern border with Russia.
"To give away the Russian part of the border also would be to cut them [the rebels] off even from humanitarian help and allow them to be surrounded,'' he said in Moscow.