During the wars in the Balkans in the 1990s, several foreign fighters, including Russian mercenaries, joined Serbian military and paramilitary forces in Bosnia and later in Kosovo. Reports and investigations at the time indicated that Russian volunteers and contractors served within Yugoslav Army structures and alongside Serbian units in various operations.

In the Bosnian war (1991–1995), Russian fighters were reportedly used partly because Serbian forces lacked trained personnel, including pilots. Some joined organized groups of foreign volunteers connected to the Bosnian Serb army.

During the Kosovo conflict in the late 1990s, witnesses and reports claimed that Russian contractors participated in operations with Serbian forces in areas such as Drenica and Deçan. In some cases, locals reported hearing soldiers speaking Russian during attacks on villages, killings of civilians, and destruction of homes.

These accounts portray the presence of foreign mercenaries as part of the broader paramilitary networks involved in the Yugoslav wars.

Reference

https://www.rtvpresheva.com/mercenaret-ruse-qe-bene-krime-ne-kosove-dhe-bosnje/