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.
Ukraine crisis: A timeline of the conflict
Ukraine crisis: A timeline of the conflict
1/22 30 November 2013
Public support grows for the “Euromaidan” anti-government protesters in Kiev demonstrating against Yanukovych’s refusal to sign the EU Association Agreement as images of them injured by police crackdown spread.
2/22 20 February 2014
Kiev sees its worst day of violence for almost 70 years as at least 88 people are killed in 48 hours, with uniformed snipers shooting at protesters from rooftops.
3/22 22 February 2014
Yanukovych flees the country after protest leaders and politicians agree to form a new government and hold elections. The imprisoned former Prime Minister, Yulia Tymoshenko, is freed from prison and protesters take control of Presidential administration buildings, including Mr Yanukovych's residence.
Genya Savilov/AFP/Getty Imageses
4/22 27 February 2014
Pro-Russian militias seize government buildings in Crimea and the new Ukrainian government vows to prevent the country breaking up as the Crimean Parliament sets a referendum on secession from Ukraine in May.
Sean Gallup/Getty Images
5/22 16 March 2014
Crimea votes overwhelmingly to secede from Ukraine and join Russia in a ballot condemned by the US and Europe as illegal. Russian troops had moved into the peninsula weeks before after pro-Russian separatists occupied buildings.
6/22 6 April 2014
Pro-Russian rebels seize government buildings in the eastern cities of Donetsk, Luhansk and Kharkiv, calling for a referendum on independence and claiming independent republic. Ukraine authorities regain control of Kharkiv buildings on 8 April after launching an “anti-terror operation” but the rest remain out of their control.
7/22 7 June 2014
Petro Poroshenko is sworn in as Ukraine's president, calling on separatists to lay down their arms and end the fighting and later orders the creation of humanitarian corridors, since violated, to allow civilians to flee war zones.
8/22 27 June 2014
The EU signs an association agreement with Ukraine, along with Georgia and Moldova, eight months after protests over the abandonment of the deal sparked the crisis.
LOUISA GOULIAMAKI/AFP/Getty Images
9/22 17 July 2014
Malaysian Airlines flight MH17 is shot down over eastern Ukraine, killing all 298 people on board. Ukrainian intelligence officials claim it was hit by rebels using a Buk surface-to-air launcher in an apparent accident.
10/22 22 August 2014
A Russian aid convoy of more than 100 lorries enters eastern Ukraine and makes drop in rebel-controlled Luhansk without Government permission, sparking allegations of a “direct violation of international law”.
11/22 29 August 2014
Nato releases satellite images appearing to show Russian soldiers, artillery and armoured vehicles engaged in military operations in eastern Ukraine.
12/22 8 September 2014
Russia warns that it could block flights through its airspace if the EU goes ahead with new sanctions over the ongoing crisis and conflict
13/22 17 September 2014
Despite the cease-fire and a law passed by the Ukrainian parliament on Tuesday granting greater autonomy to rebel-held parts of the east, civilian casualties continued to rise, adding to the estimated 3,000 people killed
14/22 16 November 2014
The fragile ceasefire gives way to an increased wave of military activity as artillery fire continues to rock the eastern Ukraine's pro-Russian rebel bastion of Donetsk
15/22 26 December 2014
A new round of ceasefire talks, scheduled on neutral ground in the Belariusian capital Minsk, are called off
16/22 12 January 2015
Soldiers in Debaltseve were forced to prepare heavy defences around the city; despite a brief respite to the fighting in eastern Ukraine, hostilities in Donetsk resumed at a level not seen since September 2014
17/22 21 January 2015
13 people are killed during shelling of bus in the rebel-held city of Donetsk
18/22 24 January 2015
Ten people were killed after pro-Russian separatists bombarded the east Ukrainian port city of Mariupol
19/22 2 February 2015
There was a dangerous shift in tempo as rebels bolstered troop numbers against government forces
20/22 11 February 2015
European leaders meet in Minsk and agree on a ceasefire in eastern Ukraine beginning on February 14. From left to right: Belarus President Alexander Lukashenko, Russian President Vladimir Putin, German Chancellor Angela Merkel, France's President Francois Hollande and Ukrainian President Petro Poroshenko.
MAXIM MALINOVSKY | AFP | Getty Images
21/22 13 February 2015
Pro-Russian rebels in the city of Gorlivka, in the Donetsk region, fire missiles at Ukrainian forces in Debaltseve. Fighting continued in Debaltseve for a number of days after the Minsk ceasefire began.
ANDREY BORODULIN | AFP | Getty Images
22/22 18 February 2015
Ukrainian soldiers repair the bullet-shattered windshield of their truck as their withdraw from the strategic town of Debaltseve. Following intense shelling from pro-Russian rebels, Ukrainian forces began to leave the town in the early hours of February 18.
Brendan Hoffman | Getty Images
“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.