MOSCOW — Russian security forces killed two suspected militants in the North Caucasus during a night-time sweep in the region plagued by an Islamist insurgency, investigators said on Tuesday.

A spokesman for local investigators said the men were killed in a gun battle with officers after refusing to surrender during a raid on a house in a suburb of the capital of Ingushetia, a region to the west of Chechnya.

The wife and child of one of them left the house before the firefight, he told Reuters by telephone.

More than a decade after federal troops defeated a separatist rebellion in Chechnya, insurgents stage frequent attacks in nearby regions fighting to establish an emirate in the patchwork of mainly Muslim provinces on Russia's south.

Two car bombs killed at least four people and wounded dozens of others on Monday, in one of the bloodiest attacks this year, in capital of Dagestan, a province bordering Chechnya to the east.

The Kremlin is worried about the spread of violence outside the region. In a suburb of Moscow on Monday, security forces killed two suspected militants alleged to have been plotting an attack in the capital.

Russian President Vladimir Putin has ordered law enforcement authorities to ensure insurgents do not attack the 2014 Winter Olympics next February in the Black Sea resort city of Sochi, which is close to the North Caucasus.