Eighteen people have been killed and more than 100 wounded in shelling in the past four days in the northeast Ukrainian city of Kharkiv, Ukraine's President Volodymyr Zelenskiy said late on Sunday.

On Sunday, five people were killed and 20 were injured when a missile and artillery fire hit the city centre and the Saltivka suburb, regional governor Oleh Synyehubov said earlier.

Reuters could not independently verify the number of people killed.

Zelenskiy said in his nightly address that Russia's shelling on Kharkiv has been constant.

"This is nothing but deliberate terror: mortars, artillery against ordinary residential quarters, against ordinary civilians," Zelenskiy said.

Synyehubov said Ukraine's armed forces had successfully engaged in counter-attacks in the Kharkiv region, recapturing two villages fully and another partially.