Avdiivka is a key Ukrainian strongpoint just northwest of the Russian-occupied city of Donetsk in the eastern Donbas region.
"The enemy launched yesterday massive assault actions with the support of armoured vehicles in Avdiivka and Mariinka directions," military spokesperson Oleksandr Stupun told Ukrainian TV.
There was no immediate comment from Russia on the fighting in the area.
The front lines in eastern Ukraine have barely shifted over the past several weeks, but the fighting has been intense, Stupun said, adding that there had been 610 artillery shellings reported near Avdiivka in just the last 24 hours.
Russia is trying to encircle the small city of Avdiivka, which now has only about 1,500 people left out of its pre-war population of some 32,000.
The fighting is reminiscent of the battle for another eastern city, Bakhmut, which fell to Russian forces in May after months of brutal urban combat.
Russia launched a renewed bid to capture Avdiivka more than two months ago and Moscow's forces have been inching forward on the flanks to try to cut supply lines.
"The fierce battles continue. Our fighters are firmly holding on defences," Stupun said.
(Reporting by Olena Harmash; Editing by Alex Richardson)
