Ukrainian servicewoman Nadia Savchenko who has been sentenced in Russia to 22 years in a penitentiary may be exchanged for Russian citizens detained in Ukraine on the "package principle", a source with knowledge of the situation told Interfax-Ukraine.

"Highly intense and fruitful negotiations are being conducted by means of every channel, and it is possible that the sides will agree on the reciprocal extradition of persons on the "package principle" - group for group," the source said.

As to Russian citizens Viktor Bout and Konstantin Yaroshenko serving time in U.S. prisons, the source said, "They also stand a chance of being exchanged on the reciprocity principle."