Ukrainian military officials say they have withdrawn some of their troops from the key eastern city of Avdiivka, where Russia is ramping up its attacks.

In a social media post on Friday, Commander Oleksandr Tarnavskiy said units with minor losses had left their positions in the southern outskirts of the city. He said the priority is to save the lives of soldiers.

He added that troops in other parts of the city will move to newly prepared positions if necessary.

Also on Friday, Ukraine's top prosecutor told reporters that Russia had recently fired at least 24 ballistic missiles suspected to be of North Korean origin.

Prosecutor General Andriy Kostin said the weapons were used in attacks on Kyiv, the eastern city of Kharkiv and elsewhere between December 30 and February 7.

But he also questioned their accuracy.

Kostin said only two of the missiles were relatively accurate, and that the rest deviated from their path, exploded in the air or landed on residential areas in Kharkiv.