Fierce fighting between Ukrainian forces and pro-Russian rebels raged on just hours before a cease-fire, signed by European leaders, was due to take effect Sunday. The fighting in eastern Ukraine cast doubts on the viability of the cease-fire, and came as the United States accused Russia of deploying heavy arms to eastern Ukraine.
Meanwhile, Kiev warned that shelling of civilians in the rebel-held areas in the east had intensified. Petro Poroshenko, Ukraine's president, said continuing bombardment of civilians by pro-Russian separatist rebels was already undermining the peace plan reached in the Belarusian capital, Minsk, on Thursday.
At least 28 civilians and soldiers were reported killed in the latest surge in fighting.
Poroshenko expressed pessimism about the prospects for the cease-fire deal, which was negotiated by the leaders of Ukraine, Russia, France and Germany.
"Unfortunately after the Minsk agreement, Russia's offensive has significantly increased. We still think that the agreement is in great danger," he said during a meeting with Hungarian Prime Minister Viktor Orban.
"After what we concluded in Minsk, these are not only attacks against civilians but also against the Minsk agreement."
The cease-fire, due to take effect at 22:00 GMT Saturday, will be the first test of the commitment by Kiev and pro-Russian separatists to the new peace plan.
A previous cease-fire in September was violated repeatedly as Ukrainian forces and the rebels both tried to gain more ground.
If it holds, the peace deal would be a partial win for both Moscow and Kiev: Ukraine retains the separatist eastern regions and regains control of its border with Russia, while Russia holds strong leverage to keep Ukraine from ever becoming part of NATO.
But prospects for the deal appeared dim, with the U.S. making fresh claims of Russia deploying heavy weapons ahead of the cease-fire.
Jen Psaki, the U.S. State Department spokeswoman, said Friday that Washington had received reports of heavy weapons being moved into eastern Ukraine from Russia over the past few days, and that more were apparently on the way.
"This is clearly not in the spirit of this week's agreement," Psaki told reporters.
Ukraine's military said that fighting remained fiercest around Debaltseve, with rebels firing missiles at the beleaguered railway hub midway between the main separatist bastions of Donetsk and Luhansk.
An Agence France-Presse news agency journalist in the rebel capital, Donetsk, said sporadic missile salvos and dozens of artillery bombardments could be heard around the city early Friday morning.
German Chancellor Angela Merkel has warned Russia that the European Union, which has already slapped Moscow with sanctions over the crisis, is not ruling out further measures if the truce fails.
The G7 nations — Canada, France, Germany, Italy, Japan, the United Kingdom and the U.S. — also voiced concern about the violence and the buildup of weapons in eastern Ukraine.
Al Jazeera and wire services