Russian forces are said to be preparing another intense ground offensive to seize Avdiivka, a Ukrainian stronghold in the eastern region of Donetsk.

A US think tank, the Institute for the Study of War, said on Wednesday, "Russian forces are likely preparing for another wave of highly attritional infantry-led ground assaults on Ukrainian positions in the Avdiivka area."

The institute says the assault units are made up largely of convict recruits.

The Ukrainian military is on guard. A spokesperson told local media on Thursday that the Russian military is believed to be reinforcing its troops before launching a new operation in the area.

Russia's defense ministry said on Thursday that its forces downed nine Ukrainian drones near the Zaporizhzhia nuclear power plant in southern Ukraine. Russia has taken control of the plant.

Russia's foreign ministry spokesperson Maria Zakharova said two drones hit a hotel near Zaporizhzhia.

She condemned Ukraine for staging "irresponsible provocations."