Russian forces have made gains in their Ukraine offensive, President Vladimir Putin said Sunday, including in Avdiivka, a symbolic industrial hub where fighting has been fierce.

"Our troops are improving their position in almost all of this area, which is quite vast," he said in an interview on Russian television, an extract of which was posted on social media on Sunday.

"This concerns the areas of Kupiansk, Zaporizhzhia and Avdiivka," Putin said, praising the army's "active defence strategy".

On Saturday, Kyiv reported "very heated" fighting around Avdiivka Saturday, saying Russian forces had "not stopped assaulting" it for days in their attempt to surround it.

Ukraine last week said Russia had stepped up assaults on the frontline city, which lies just 15 kilometres (nine miles) from Moscow-held Donetsk.

Avdiivka has been a symbol of Ukrainian resistance since 2014, after it briefly fell to Russian-backed separatists.

It has since marked the frontline and was regularly bombed even before the offensive began in February 2022.

Russian forces now control territory to the east, north and south of Avdiivka in a bid to push Ukrainian forces further from Donetsk.

Some 1,600 civilians are believed to be in the city, which had a pre-war population of 31,000.

Ukrainian President Volodymyr Zelensky had said Kyiv was holding its ground in Avdiivka, but Moscow has previously claimed its positions had improved there.

On Sunday, Kyiv's army said Russian attacks had been "repelled" in the area and remained "without success".

Several analysts, using open source images of the assault on Avdiivka posted on social networks, have noted the Russians appear to suffering major losses of military materiel.

Russia's intensified assault on Avdiivka has come after four months of a Ukrainian counter-offensive, which has been slower than expected.

Putin on Sunday repeated that the counter-offensive had "totally failed".

"We know that in some combat zones, the enemy is preparing new offensive operations," he said.

"We see it, we know it. And as a consequence we are reacting."

Russian strikes have left four people dead and three wounded since Saturday in the eastern region of Kharkiv and Kherson, in the south, local authorities said.

AFP