An area on the outskirts of Makhachkala, the capital of Dagestan, has been locked down since Wednesday's suicide car bombing at a police station as authorities hunted for the masterminds and their accomplices.

Dagestan, Ingushetia and Chechnya, all predominantly Muslim republics in the North Caucasus region, saw a sharp rise in violence last year, with many of the nearly daily attacks targeting police and other officials. Suicide bombings, once rare, are occurring with growing frequency.

The violence sweeping the impoverished southern region is increasingly being described as a civil war between Kremlin-supported administrations and Islamic militants. Widespread abuses against civilians by police, including abductions, torture and killings, have helped to swell the ranks of the militants.

Authorities early Thursday gunned down two suspected insurgents who had barricaded themselves inside a house, according to Dagestan police spokesman Mark Tolchinsky.

An hours-long shootout — during which the militants hurled grenades at police — ended when police stormed the building, Tolchinsky said. Two police were wounded in the crossfire, Tolchinsky said.

He named one of the slain militants as Ismail Ichakayev, a man reportedly wanted for masterminding several bombings and other attacks on officials.

Tolchinsky refused to confirm reported comments by a spokesman for federal investigators in Moscow that the militants had planned Wednesday's attack.

The suicide car bomber hit a police station on Wednesday at a time when 150 officers were lined up outside on roll call.

City police chief Col. Shamil Guseinov said the six officers who died had prevented a far greater catastrophe by blocking the bombers' entry into the compound.