Moscow denied on Monday that the two fighters captured by Ukrainian troops over the weekend are serving in Russian special forces, and insisted that they voluntarily participated in the Donbass armed conflict.

"The Russian citizens, Alexander Alexandrov and Eugeny Yerofeev, captured in Lugansk region by the Ukrainian Security Service (SBU), have not been in active military service in Russian armed forces at that moment of detention," Interfax news agency quoted Defense Ministry spokesman Igor Konashenkov as saying.

Konashenkov admitted that the two Russians had actually served in the special forces in the city of Togliatti (in the mid-Volga Samara area) before they voluntarily joined the armed conflict in the eastern Ukraine on the insurgents' side.

He demanded that Ukraine "stop torturing" the wounded fighters who, he believed, had claimed to be in active service under pressure from SBU.

Demanding the soonest release of the two Russians, Konashenkov reminded that "dozens and hundreds" of Ukrainian servicemen have been captured in the Russian territory near the border within the conflict zone and Russia has returned all of them.

An online video published on Sunday showed one of the two detainees introducing himself as a Russian soldier serving in the special forces.

There are reports saying that they were captured on Saturday in the town of Shchastye north of Lugansk city.

Earlier on Monday, Kremlin spokesman Dmitry Peskov has denied presence of any Russian troops in the conflict-engulfed eastern Ukraine.