Ukraine and Russian-backed rebels fought fiercely for control of a strategic railway junction on Friday despite a new peace deal brokered by Germany and France.
A cease-fire is due to come into effect from Sunday under the agreement, which also envisages a withdrawal of the heavy weaponry responsible for many of the more than 5,000 casualties in the conflict that broke out almost a year ago.
Both sides accused each other of killing civilians. Two people were killed and six wounded when a shell hit a packed cafe in the Kiev-controlled town of Shchastya near rebel-held Luhansk in eastern Ukraine, a local official said, adding that other shells had struck elsewhere in the town.
"The town's heating system is broken, power lines are damaged as well as the water supply ... So this is how a comprehensive cease-fire is prepared for," the head of the Kiev-controlled administration, Hennadiy Moskal, said online.
The rebels accused Ukrainian forces of shelling the separatist stronghold of Donetsk and the town of Horlivka, where they said on their website that three children had been killed.
They gave no details, and it was not immediately possible to verify any of the reports, which followed threats of further sanctions on Moscow from the United States and Europe if the rebels seize more territory.
The deal, sealed in person by the leaders of Germany and France on Friday after more than 16 hours of intense, overnight talks in Minsk, capital of Belarus, with the Russian and Ukrainian presidents, was soon overshadowed by the clashes on the ground in rebel-held eastern Ukraine.
"This night was not a calm one," the Ukrainian military said on Friday. "The enemy shelled positions of the 'anti-terrorist operation' forces with the same intensity as before."
A Ukrainian military spokesman said eight soldiers had been killed and 34 wounded in the past 24 hours.
Fighting had been particularly intense around Debaltseve, a railway junction linking the two main rebel areas, where separatists had used rockets and artillery to attack government forces holding the town, the statement said.
Away from the battlefield, disagreements surfaced over whether a rebel amnesty or the release of a Ukrainian pilot detained by Russia were part of the cease-fire deal.
Western diplomats said the European Union would go ahead on Monday with a new round of sanctions against 19 Ukrainian separatists and Russians, despite the cease-fire.
NATO and the United States said the fighting ran counter to the spirit, if not the letter of the agreement and U.S. officials said further sanctions were still on the table.
At an EU summit in Brussels, the leaders of Germany, France and the European Council also said new sanctions were possible.
On Friday, the Kremlin said the four leaders remained in touch over the Ukraine crisis, and that he expected a phone conversation in the coming days, RIA-Novosti reported.
Spokesman Dmitry Peskov also said Moscow expected all points of the deal to be implemented, but that Russia had not promised to free detained Ukrainian pilot Nadezhda Savchenko. Savchenko's case would be decided by a Russian court, he said.
Ukraine, for its part, said it had not agreed to an amnesty for all rebels, drawing an angry response from the separatists.
Sanctions by the EU and United States have piled intense economic pressure on Russia's economy, which has also been hit by a collapse in oil prices.
Russia's economy minister said he hoped sanctions would be lifted soon.
Vast "Buffer Zone"
On Thursday, German Chancellor Angela Merkel described the agreement with Russia on Ukraine as a good start but said undertakings must now be respected.
Ukraine reported a new, mass influx of Russian armor into rebel-held eastern Ukraine as the agreement was being finalized.
The deal calls for the withdrawal of heavy weapons from the front line when and if the cease-fire has taken hold, and constitutional reform to give eastern Ukraine more autonomy.
The rebels have advanced far past an earlier cease-fire deal, agreed in September, and the new agreement appears to envisage them pulling their guns back around 75 km, to take them back behind it, while Ukrainian guns would move 25 km back.
This would leave a buffer zone some 50 km wide, a challenge for the monitors from the Organization for Security and Cooperation in Europe who are expected to patrol it.
It also appears to take yet more territory outside Kiev's control.
The White House, under pressure from Congress to provide arms to the stretched Ukrainian military, said the deal was "potentially significant" but urged Russia to withdraw soldiers and equipment, and give Ukraine back control over its border.
Russia denies arming the rebels and sending troops to fight alongside them, despite what Ukraine and its Western allies say is overwhelming evidence.