Russian forces were Tuesday trying to encircle the eastern frontline Ukrainian town of Avdiivka, an official said, adding it was being heavily bombed.
Kyiv's forces have managed to cling on to Avdiivka despite repeated Russian strikes. The town lies just north of the Russian-controlled city of Donetsk, which was captured by separatist forces in 2014.
"For over a year, there has been the danger that (Avdiivka) can be occupied, but now the situation has worsened rapidly," said Vitaliy Barabash, head of the town's administration.
Russian troops launched an artillery attack in the morning and were firing incessantly, he said.
A local police officer, Pavlo Diachenko, told AFP that Avdiivka, now home to less than 2,000 people, was undergoing a "severe artillery attack".
Kyiv launched its bid to wrest back territory controlled by Moscow in June, after stockpiling Western-supplied weapons and recruiting assault battalions.
But in some areas it has faced a Russian pushback, including in the northeast region of Kharkiv where Moscow's forces claimed to have gained ground.