One serviceman was wounded when unknown...

"The incident occurred at about 19:45 Moscow time [16:45 GMT]. A serviceman was wounded," a spokesman for investigators said.

Law enforcement agencies said the assailants fired a grenade launcher and then opened fire with assault rifles.

An investigation is underway.

Russia"s mainly Muslim and ethnically diverse North Caucasus republics have been swept by an upsurge of violence recently, which has also swept neighboring regions, where hundreds of people have been killed in militant attacks and skirmishes between security forces and gunmen.

Moscow announced an end to its decade-long antiterrorism campaign against separatists in Chechnya in April 2009, but has since had to step up the fight against militants as skirmishes and attacks on police and other officials have continued.

ROSTOV-ON-DON, January 8 (RIA Novosti)