Russia pounds frontline positions with artillery, launches 400 strikes in East: Volodymyr Zelenskyy

"In the Luhansk region, we are slowly moving forward while fighting. As of now, there have been almost 400 artillery attacks in the east since the start of the day," he continued.

Zelenskyy also said troops in the south were "consistently and very calculatedly destroying the potential of the occupiers" but gave no details.

Kyrylo Tymoshenko, deputy head of Zelenskyy's administration, said late on Sunday that Russian forces fired at a residential building in the Kherson region, in southern Ukraine.

"There may be people under the rubble. Emergency services are working at the scene," Tymoshenko said on the Telegram messaging app.

The region's recently retaken capital, the Kherson city, remains without electricity, running water or heating.

Kyiv said on Saturday that about 60 Russian soldiers had been killed in a long-range artillery attack in the south, the second time in four days that Ukraine has claimed to have inflicted major casualties in a single incident.