The situation around eastern Ukraine's frontline city of Chasiv Yar is "difficult and tense", the army said on Sunday, adding that the Russian invaders were now "in retreat".

Russian forces have unleashed "constant fire" in the area in recent days seeking to seize the city's dominant heights.

Chasiv Yar lies less than 30 kilometres (18 miles) southeast of the regional town of Kramatorsk, an important rail and logistics hub for Ukraine's army.

"The situation is difficult enough and tense," said Oleg Kalashnikov, spokesman for an army brigade deployed in the area.

"The Russian are trying to carry out assaults directly on the small towns of Bogdanivka and Ivanivske, outside Chasiv Yar," Kalashnikov told Ukrainian television.

"They are also trying to carry out offensive actions between the two places," he added.

The Russian army was "using infantry backed by armoured fighting vehicles", and "warplanes".

"But all their attacks have been repelled. They are in retreat," the spokesman said.

On Friday, Russian occupying authorities said Moscow's troops were advancing towards Chasiv Yar in the eastern Donetsk region.

Both Ukrainian and Russian military bloggers with links to the armed forces said Russian troops had reached the outskirts of the town.

Kalashnikov on Sunday stressed the strategic importance of Chasiv Yar, 20-kilometres west of Bakhmut, which was flattened by months of artillery fire before it was captured by Moscow last May.

Russia has recently secured its first territorial gains since seizing Bakhmut and is now trying to press onwards against Ukrainian units hobbled by delays in the supply of vital Western military aid.

If Russia takes the devastated town of Chasiv Yar, where 770 people remain out of a pre-invasion population of 13,000, it "will be able to bombard Kostiantynivka", 10 kilometres to the southwest, Kalashnikov warned.

"The enemy will also be able to threaten logistics routes (between Kostiantynivka, Slovyansk and Kramatorsk)," he said, adding that the last two places could also come under direct attack.