Russian security forces have killed six extremist militants with suspected ties to foreign terrorists in the country’s volatile North Caucasus, the anti-terror committee said on Monday.

Russian security forces have killed six extremist militants with suspected ties to foreign terrorists in the country's volatile North Caucasus, the anti-terror committee said on Monday.

Special forces launched an anti-terror operation overnight in the southern Russian city of Nalchik, surrounding militants that had barricaded themselves in an apartment building.

"Six bandits were neutralized as a result of the clashes," Russian news agencies cited a spokesperson of the national anti-terrorism committee as saying on Monday.

"Negotiations with the armed group lasted a few hours. The militants refused to lay down their arms and opened fire against law enforcement officials."

Authorities claimed the armed group fostered ties with an "international terror organization" which they did not name, and accused it of a number of crimes, including the murder of a police officer.

On Sunday, security forces said they had killed eight extremist militants, members of an insurgency group that pledged allegiance to ISIL earlier this year.

Some 2,000 Russian nationals are thought to have joined the ranks of ISIL.

Clashes between extremist militants and Russian armed forces are an habitual occurrence in the North Caucasus, especially in the republics of Dagestan and Chechnya.

More than 340 people were killed last year as a result of armed conflict in the region, independent news site Kavkazsky Uzel reported.