The battle for Sievierodonetsk is being waged house to house as Ukrainian fighters hope for the delivery of heavy weapons that might "turn the tide," a Ukrainian commander said on Thursday.

Petro Kuzyk, commander of the Svoboda (Freedom) National Guard battalion, said street fighting in the small industrial city in eastern Ukraine was at times raging under heavy Russian artillery barrages that endangered troops on both sides.

Reuters could not verify the situation on the ground in what has become a pivotal battle in Russia's war in Ukraine. Moscow did not comment on Kuzyk's remarks and has said Ukraine is suffering significant losses in the Donbas region where Sievierodonetsk is located.

"We fight for every house and every street," Kuzyk told national television, describing fighting in which Ukrainian fighters had gone from "blind defence to small counter-offensives in some areas.

"Yesterday was successful for us. We went on a counterattack and in some areas we managed to push them back by one or two blocks. In others we pushed them back literally by one or two houses."

Kuzyk said Ukraine had hoped Russian forces would reduce the intensity of their artillery fire when street fighting began.

"When we imposed street fighting on them, it worked for some time - they (their artillery) did not know where they were and where we were. But now they are simply covering both their own troops and our units with artillery fire," he said.

Kuzyk said Ukraine's forces had a "catastrophic" lack of systems to counter Russian artillery and needed "serious technology", or heavy weapons, to strike back at the Russians.

Appearing to rule out a withdrawal to the twin city of Lysychansk on the opposite bank of the Siverskyi Donets river, he said: "There is an order to hold positions and we hold them."

Moscow says its "special military operation" in Ukraine is intended to disarm and "denazify" its neighbour and denies deliberately targeting civilians. Ukraine and its allies call the invasion an unprovoked war of aggression.