Ukraine says five of its troops have been killed in clashes with pro-Russia separatists in some of the worst fighting to hit the eastern Donbas region in months.
The headquarters for the country's Antiterrorism Operations said six soldiers were wounded in the battle near Svitlodarsk, which appeared to be aimed at controlling the strategic town of Debaltseve.
In a post to its Facebook page, the agency's press center said around 20 insurgent fighters had been killed in the clashes, which erupted before dawn on December 18 and lasted around two hours.
Fighting included heavy artillery and large-caliber weaponry.
It said fighting was reported near the village of Kalynivka, closer to Debaltseve, and shelling also took place near Mariupol, on the Sea of Azov coast.
Russian and local news agencies affiliated with the separatist group known as the "Luhansk People's Republic" reported similarly heavy fighting, but said losses among Ukrainian government troops were much higher.
Home to a strategic railway junction, Debaltseve was the scene of major fighting in early 2015, ending in February when thousands of Ukrainian troops withdrew.
The battle gave way to cease-fire accords signed in February 2015, known as the Minsk accords.
Signed by Ukrainian President Petro Poroshenko and Russian leader Vladimir Putin, they were meant to end one of Europe's bloodiest conflicts in decades.
But the cease-fire has been repeatedly broken by both sides and low-level fighting has pushed the death toll to nearly 10,000, according to United Nations figures.
With reporting by Interfax and TASS