But Lugansk's regional governor Sergiy Gaiday said they expected a major counter-attack from Russian forces in the coming days.

"Our armed forces have cleaned half" of the industrial hub of Russian troops, Gaiday said in an interview posted on his official social media channels.

"Half of the city is actually controlled by our forces."

Severodonetsk is the largest city still in Ukrainian hands in the Lugansk region, which is part of Donbas. Russian forces have been gradually advancing there in recent weeks after having retreated or been pushed back from other areas, including around the capital Kyiv.

After being pushed back by a Russian offensive on the city, Ukrainian troops have steadily clawed back ground there.

Gaiday said that Russian forces had been tasked with gaining control of the city by Friday, as well as a key transport artery connecting two other nearby cities, Lysychansk and Bakhmut.

"We expect in the near future that all the reserves that they now have access to -- all the reserves, all the personnel that they have -- they will throw to perform these two tasks," Gaiday said.

"In the next five days, there will be a large increase in the number of shellings from heavy artillery," from the Russian side.