The men are facing charges of terrorism-related activities, illegally crossing the border, illegally transfering weapons and ammunition and the illegal possession of weapons, among other charges.
The source said that international agreements do not assume the swapping of prisoners serving terms in countries other than their home country and that each case is handled separately.
“It is possible to make extraditions in groups between one another [Kiev and Moscow], but we don’t have any plans of doing this,” the source said.
Savchenko was sentenced in late March to a 22-year jail term in Russia for her part in killing Russian journalists in eastern Ukraine. She subsequently refused to appeal the ruling. The Ukrainian authorities, however, have been trying to find ways for her possible return to her homeland, including through an exchange for Russian nationals held in Ukraine.