Ukraine conflict: Crucial summit goes through the night
The Russian and Ukrainian presidents have been meeting all night in Belarus to try to secure a peace deal.
Few details have emerged about their four-way meeting with the leaders of France and Germany. But a Ukrainian presidential aide posted on Facebook that there was a battle of nerves.
Before the talks began, the Ukrainian President Petro Poroshenko said achieving a ceasefire was essential.
Thousands of people have been killed in the fighting in the east of Ukraine.
German Chancellor Angela Merkel and French President Francois Hollande are leading the peace initiative in Minsk.
There was little warmth as Russian President Vladimir Putin shook hands with Mr Poroshenko.
Russia has been accused of arming and reinforcing pro-Russian rebels in east Ukraine - a claim it denies.
The talks are set to focus on securing a ceasefire, withdrawal of heavy weapons and creating a demilitarised zone.
At the scene: Lyse Doucet, BBC chief international correspondent
The images tell you an awful lot. The Ukrainian and Russian presidents barely looked at each other when they were forced to shake hands. At a family photo of the leaders, not a single person was smiling. There was even an image of Vladimir Putin inside the negotiations snapping a pencil in two.
In the end, what it will come down to is what the Ukrainian President, Petro Poroshenko, is willing to accept in terms of a compromise and what Russia is willing to offer.
In broad terms what Ukraine, backed by the West, wants is to restore Ukraine's territorial integrity, including control of the border with Russia. But what the separatists in eastern Ukraine, backed by Russia, want is to remain in charge of the territory that is now under their control.
The best that anyone says can be achieved is a freezing of the conflict.
On the ground in eastern Ukraine's Donetsk and Luhansk regions, Wednesday saw new attacks:
- Heavy shelling was reported by bloggers in the rebel-held city of Luhansk; a freelance reporter on the ground, Pierre Sautreuil, reported (in French) that a rebel military base seemed to be the target of one bombardment in the south-east of the city
- At least one person died when a hospital was shelled in the rebel-held city of Donetsk, bringing the day's toll from shelling there to at least six.
- Rebel forces near the strategic town of Debaltseve bombarded government forces with mortars a day after the government reported the deaths of 19 soldiers in the area
While the Ukrainian government is seeking a demarcation line based on the failed ceasefire agreed on 5 September in Belarus, 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 31 January and 5 February.
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.
US President Barack Obama has refused to rule out supplying "lethal defensive weapons" to Kiev if diplomacy fails, but Russia says that would worsen the crisis.
Rival agendas at Ukraine talks
Ukraine: Restore government authority over breakaway areas, though Donetsk and Luhansk regions could get greater self-rule; disarm rebel forces; withdrawal of Russian troops; restore Kiev's control over Ukraine-Russia border; full prisoner exchange.
Pro-Russian rebels: Separation from rest of Ukraine and recognition of "people's republics" of Donetsk and Luhansk; no disarmament of separatist forces; amnesty for separatist leaders.
Russia: Legal guarantees for rights of Russian-speakers in eastern Ukraine; full autonomy for Donetsk and Luhansk in a federal system - not necessarily independence; no return of Crimea to Ukraine; withdrawal of Ukrainian troops from combat zone.
EU and US: Restore Ukraine's territorial integrity; end Russian intervention in eastern Ukraine - withdrawal of all Russian troops and heavy weapons; effective monitoring of Russia-Ukraine border and demilitarised zone between the combatants; full democracy in Donetsk and Luhansk.
Ukraine's war: The human cost
- At least 5,486 people people killed and 12,972 wounded in eastern Ukraine but true numbers could be much higher
- Fatalities include 298 people on Malaysia Airlines flight MH17 shot down on 17 July
- 5.2 million people estimated to be living in conflict areas
- 978,482 internally displaced people, including 119,832 children
- 600,000 fled to neighbouring countries, of whom more than 400,000 have gone to Russia
Source: Figures from UN report, 6 February
Please include a contact number if you wish to be contacted by a BBC journalist.