Yury Karasyov, the head of the investigative department of the Russian Interior Ministry, said the arrests were carried out last week in the Moscow region on a tip-off from Ukrainian authorities and with Ukrainian officers in attendance.
He said the suspects' extradition to Ukraine will be decided within the next couple of months.
The killings were allegedly carried out between 1991 and 2002 in Ukraine's eastern region of Donetsk.
Another nine suspected members of the same group had been arrested earlier in Ukraine.
(AP, AFP, Interfax-Ukraine)