Russian troops have entered the eastern Ukrainian city of Avdiivka, which has been under siege since mid-October, the Ukrainian army announced Thursday, adding that fighting is raging in the area.

Russian forces are attempting to capture Avdiivka, home to a large coke plant and seen as a gateway to the occupied city of Donetsk, 20km to the east.

“I can confirm that. Yes, there are clashes inside the city,” Ukrainian military spokesman Dmytro Likhovy told state television. He claimed that Russian troops have massed north of the city, seeking to cut off the only supply route to Ukrainian forces defending Avdiivka. However, he described the situation as “difficult, but controlled”.

Mayor Vitaly Barabas said that Avdiivka now has 941 residents left of the approximately 32,000 that the city had before the war. Avdiivka was briefly controlled by pro-Russian separatists in 2014, but was recaptured by the Ukrainian army, which turned it into a fortress. Speaking on Ukrainian television, Barabas had not hidden his concern earlier because the situation was becoming more and more difficult for the troops defending his city.

A potential capture of Avdiivka will be welcomed by the Kremlin ahead of next month’s Russian elections in which President Vladimir Putin is virtually certain to secure re-election.