Peace talks on Ukraine have broken up after more than four hours with Kiev's envoy accusing separatist envoys of undermining the meeting by making ultimatums and refusing to discuss plans for a ceasefire, according to reports.
Ukraine's representative, former president Leonid Kuchma, was quoted by Interfax news agency as saying that the two separatist officials present had delivered ultimatums and refused "to discuss a plan of measures for a quick ceasefire and a pull-back of heavy weapons".
He also reproached the two main separatist leaders in eastern Ukraine, who signed key agreements in Minsk last September, for failing to attend Saturday's follow-up meeting of the "contact group", which also involved a Russian envoy and an official from the Organisation for Security and Cooperation in Europe.
Up until Saturday, the sides had held only one inconclusive meeting since agreeing on a ceasefire last September as part of a 12-point blueprint for peace. Much-violated from the start, that truce collapsed completely with a new rebel advance last week.
Both sides have accused each other of deadly artillery and mortar strikes on civilian targets in the past two weeks, including one on a cultural centre in the main regional city of Donetsk on Friday which killed at least five people waiting for humanitarian hand-outs.
Since September, the separatists have set up self-proclaimed "people's republics" while their forces, which Kiev says are supported by 9,000 Russian regular troops, have seized more than 500 square kilometres of territory.
Heavy shelling continued on Saturday in Ukraine's eastern regions as the separatists sought to tighten a circle around government forces clinging on to control of the strategic rail and road junction of Debaltseve.
Regional police chief Vyacheslav Abroskin, in a Facebook post, said 12 civilians had been killed on Saturday by separatist artillery shelling of the town, which lies to the northeast of Donetsk.
Defence Minister Stepan Poltorak said 15 Ukrainian soldiers had been killed and 30 wounded in clashes across the east.
"The toughest situation is in the Vuhlehirsk area where the terrorists are trying to seize the town and occupy positions to move forward and encircle Debaltseve," military spokesman Andriy Lysenko said in a separate briefing.
Debaltseve is on the main highway linking Donetsk and the other big rebel-controlled city of Luhansk and is also a vital rail link for goods traffic from Russia which Kiev accuses of arming the rebels.
More than 5,000 people have been killed in the Ukraine conflict which erupted last April following Russia's annexation of Crimea in response to the ousting of a Moscow-backed president in Kiev by street protests.