One of the attackers was killed. Security forces have detained a second suspect.
Russian troops have been battling separatist militants in the nearby Russian republic of Chechnya for more than a decade. Two days of fighting near the Chechen border last week left 12 suspected rebels and seven policemen dead.
The Chechnya Conflict
The aftermath of a December 2002 Chechen resistance attack on the main government building in Grozny (epa)