"Up to 80 Polish mercenaries, 20 armoured combat vehicles and eight Grad multiple rocket launchers were destroyed in precision strikes on the Megatex zinc factory in Konstantinovka" in the Donetsk region, the Russian defence ministry said in a statement, which could not be independently verified.

The region, claimed by Russia, has been the theatre of combat since Moscow began its offensive in Ukraine in late February.

The Russian ministry did not state when the strikes took place. In its statement, the ministry added that "more than 300 Ukrainian troops and foreign mercenaries as well as 35 heavy weapons were destroyed in the space of a day in Mykolaiv," a Black Sea city in southern Ukraine.

Russia describes as "mercenaries" foreign volunteers fighting with Ukrainian forces.

In April the defence ministry said some 30 Polish "mercenaries" had been killed in the northeastern city of Kharkiv.