Moscow has made a number of gains on the frontline in recent months, pressing their advantage as Kyiv struggles with shortages of vital munitions from its Western allies.

"The situation with regard to Chasiv Yar has been difficult and tense, not for the first day," said Oleg Kalashnikov, press officer for Ukraine's 26th Artillery Brigade.

"Today it is the main focus for the enemy in its assault operations. It is trying to push through our defenses in order to reach Chasiv Yar," he said.

He also said Russia had increased its use of powerful guided bombs in the area, and was "dropping them on populated areas and on our fortified positions."

Ukraine has been forced onto the defensive in the past few months as it struggles with ammunition shortages and a hold up to a $60 billion aid package from Washington.

Its ground forces commander warned last week Russia was building a group of over 100,000 soldiers in advance of what may be a major offensive this summer.