Ukrainian President Volodymyr Zelenskiy said on Tuesday the defence of the shattered eastern city of Avdiivka was key to Kyiv's war plans, with heavy Russian losses there likely to undermine Moscow's conduct of the broader conflict.

Ukraine's President Volodymyr Zelenskiy.

Zelenskiy's chief of staff, meanwhile, acknowledged for the first time that Ukraine's forces in southern Kherson region had established a foothold on the eastern bank of the Dnipro River, potentially opening a new line of attack towards Crimea.

Russian troops abandoned the western bank a year ago and took up positions on the eastern side from which they have been regularly shelling towns and villages opposite.

Moscow's forces have focused on eastern Ukraine since failing to advance on Kyiv in the first days of the February 2022 invasion. They have taken aim at Avdiivka since mid-October and officials from the town, which had a pre-war population of 32,000, say not a single building remains intact.

Zelenskiy, in his nightly video address, said Russian assaults in the eastern Donetsk region including Avdiivka had been "very intense".

"Russia is already losing men and equipment near Avdiivka faster and on a larger scale than, for example, near Bakhmut," he said, referring to months of heavy fighting that culminated in Russian forces capturing the eastern town of Bakhmut in May.

"Withstanding their pressure is extremely difficult ... The more Russian forces that are destroyed near Avdiivka, the worse the overall situation will be for the enemy and the overall course of this war."

Official Russian accounts of fighting in the east made no mention of Avdiivka, though prominent Russian war blogger Rybar said there had been "some headway" in positions around the town.

Russia's Defence Ministry said Moscow's forces had repelled five attacks around villages near Bakhmut recaptured by Ukraine since May. It said Ukraine had suffered 300 dead and wounded.

Reuters could not verify accounts from either side.

Bakhmut lies about 50 km (31 miles) north of Avdiivka, which is only 20 km west of the Russian-held regional capital of Donetsk.

Ukrainian military spokesperson Oleksandr Shtupun said fighting was heaviest south of Avdiivka.

"Over the last three days, the occupiers have actively used guided aviation bombs in Donetsk region, particularly around Avdiivka," Shtupun told national television. Ukrainian forces, he said, had repelled 18 Russian attacks over the past 24 hours.

FOOTHOLD IN THE SOUTH

The acknowledgement by Ukrainian presidential chief of staff Andriy Yermak that Kyiv's forces were established on the Dnipro's eastern bank followed weeks of contradictory reports.

"Against all odds, Ukraine's Defense Forces have gained a foothold on the left (east) bank of the Dnipro," Yermak said in an address to the Hudson Institute think-tank in the United States. The remarks were posted on Zelenskiy's website.

"Step by step, they are demilitarizing Crimea," he added, referring to the peninsula Russia seized in 2014. "We have covered 70% of the distance. And our counteroffensive is developing."

As Ukraine's four-month-old counteroffensive secures only incremental gains, Ukrainian officials have been cautious in describing the activities of their forces on the east bank.

Russia's military said last week its forces had thwarted a Ukrainian attempt to forge a bridgehead on the eastern bank and on nearby islands, killing around 500 Ukrainian soldiers.

In a highly unusual incident on Monday, two Russian state news agencies published alerts saying Moscow was moving troops to "more favourable positions" east of the Dnipro River in Ukraine, only to withdraw the information minutes later.

Russia has sometimes used similar phrasing about moving troops to more advantageous positions to describe retreats.