Russia's army said Saturday that some Ukrainian military units were withdrawing from the key city of Severodonetsk in eastern Ukraine.

"Some units of the Ukrainian army, having suffered critical losses during fighting for Severodonetsk, are pulling out towards Lysychansk," Severodonetsk's twin city, which sits just across a river, the defense ministry said in a statement. It added, however, that some Ukrainian fighters were still in the city.

The Ukrainian side has not responded to this claim.

(With input from AFP)