A new round of peace talks have started between the Ukrainian government and pro-Russian rebels after being stalled by the deaths of at least 40 people in 24 hours of fierce fighting.
Both civilians and soldiers have fallen victim to the latest violence, which shows no sign of calming even as Ukrainian and separatist representatives gather in Minsk.
The city in Belarus was also the scene of a long-discarded 12-point truce agreed after a ceasefire in September.
Ukrainian officials say 15 soldiers and 12 civilians have died in the past 24 hours, while rebels reported 13 casualties in areas they control, both military and civilian.
The separatists claimed to have seized another town, Vuhlehirsk, but Ukrainian officials denied this, admitting that nearby Debaltseve was now "partially controlled" by the rebels.
Both sides have accused each other of deadly artillery and mortar attacks on civilian targets in the past two weeks, including one a community centre in rebel-held Donetsk city yesterday which killed five people queuing for humanitarian aid.
Heavy shelling continued there on Saturday as the separatists sought to tighten a circle around government forces clinging on to control of the strategic rail and road junction of Debaltseve.
Vyacheslav Abroskin, a Ukrainian government official, said 12 civilians had been killed on Saturday by separatist artillery shelling of the town, which lies to the north-east of Donetsk.
Debaltseve is on the main road linking Donetsk and the second-largest rebel-controlled city of Luhansk. It is also a vital rail link for goods traffic from Russia.
Ukrainian Defence Minister Stepan Poltorak said 15 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,” a military spokesperson said.
“Vuhlehirsk is under the partial control of terrorists,” said Semen Semchenko, commander of the pro-Ukrainian Donbas Battalion.
“We retain some of our strong points. A terrorist attack occurred yesterday, after artillery fire struck tanks at the positions of our forces. Over the past few weeks this group of terrorists had infiltrated into the city disguised as civilians and [we were] hit from the rear.
“In Vuhlehirsk there are enemy armoured vehicles, sniper nests in people’s homes, the city is actively being reinforced.”
The rebels were also continuing to threaten Mariupol, a strategic port city where 30 civilians died in shelling last weekend.
Ukrainian former president Leonid Kuchma, a Russian diplomat and an Organization for Security and Cooperation in Europe (OSCE) official - met at a state residence in the Belarussian capital Minsk today, where they were joined by two separatist officials.
The Chief Monitor of the OSCE Special Monitoring Mission to Ukraine, Ambassador Ertugrul Apakan, had condemned the shelling of densely populated civilian areas in eastern Ukraine.
“Yet again, innocent civilians have been impacted by the crisis, and yet again we are seeing more bloodshed,” he added, saying investigators were establishing the facts in Donetsk.
“It should be understood that the main outcome of such violence is a surge in human suffering. I urge all sides to exercise maximum restraint, and fully assume their responsibility to prevent further displacement and suffering and to redouble their efforts to reach a political settlement.”
The September Minsk peace plan called for an immediate ceasefire, tighter control of the Russia-Ukraine border, through which Kiev says Moscow is funnelling fighters and equipment, the freeing of prisoners held by both sides, elections and devolved political power to Ukraine’s regions.
Separatists already run two “people’s republics” in the Donetsk and Luhansk oblasts, where fighting has raged since they deposed the local governments in April, with government forces trying to re-gain control.
Their forces, which Kiev claims are supported by 9,000 Russian regular troops, have seized more than 190 square miles of territory beyond that agreed in the Minsk talks and threaten to overrun the east's two main regions entirely.
Russia denies what several Western countries have claimed is proof that its troops are fighting on behalf of the separatists and providing them with military equipment.
More than 5,000 people have been killed and 1.2 million displaced in the the conflict, which erupted in April following Russia's annexation of Crimea in response to the ousting of Moscow-backed president Viktor Yanukovych in Kiev by months of street protests.
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