"Presumably, there may be mercenaries among the blocked militants," a source at the combined forces' headquarters told Interfax.

"As far as we know, this group is subordinated to Doku Umarov, a co-leader of militants operating in the North Caucasus," the source said.

Chechen terrorist Umarov is wanted in Russia over alleged murders, kidnapping, and terror attacks, including the Beslan school siege in 2004.

The joint Chechen-Ingush police operation has been going on for several days. It was launched after a suicide attack in front of the Interior Ministry building in the Chechen capital Grozny on May 15, when four people were killed and five seriously injured.

The source told Interfax that four militants have been killed since then; one of them was a mercenary from Azerbaijan.

A policeman was injured in an explosion of a land mine while searching for the militants in a forest.

Earlier this year, Chechen President Ramzan Kadyrov announced amnesty to all those hiding in the forest. He called them to return to peaceful life, promising no punishment would follow. But after the Friday's events the message was, 'no mercy!'