Ukraine's positions around the frontline city of Avdiivka, in the eastern Donetsk region, are "protected", President Volodymyr Zelensky said in his evening address Sunday.

The city has been the center of intense fighting in recent weeks as each side struggles to advance along the frontlines. Ukraine's general staff said on Friday that Russia had stepped up its military assault on Avdiivka in an ongoing bid to encircle and capture it.

"The Avdiivka and Maryinka directions are particularly tough," Zelensky said. "Numerous attacks by Russians. But our positions are protected."

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

It lies just 15 kilometers (nine miles) from the Moscow-held city of Donetsk, the capital of the Donetsk region that Russia said last September it was annexing.

Ukrainian soldiers had been bracing for a new assault after a failed Russian offensive earlier this month using columns of armored vehicles and tanks from three sides.

Built around a huge coke plant, Avdiivka had a pre-war population of around 30,000 people.

Around 1,600 remain, according to local authorities, living in basements converted into bomb shelters.

The city center has been all but destroyed through daily Russian artillery shelling and a months-long aerial bombing campaign.