Russia has asked a number of European countries, including the Baltic states, to look into their citizens fighting for the Ukrainian government against pro-Russian separatists.
The accusations concern Azov paramilitary battalion, which includes foreign volunteers, which Russia says has volunteers from Sweden, Finland, the Baltics and France.
According to Russia, the battalion is financed Ihor Kolomoyskyi, the governor of Dnipropetrovsk Oblast, in eastern Ukraine, and one of the nation's richest men.
Although battalion commanders have denied such claims, the BBC recently ran a story on the Azov Battalion, also saying the group has extreme right-wing tendencies.
Many of separatists, fighting against Ukrainian forces, have arrived from Russia and other ex-Soviet states, including many, if not most, of the separatist leaders. Western nations have accused Russia of supplying the volunteers with arms.
Russian allegations of Baltic mercenaries have long been a bogeyman, going back to the time of the first Chechnya war, when rumors of "blond bombshells" - a mythical elite squad of female Baltic combatants - were floated in one less refined claim.