MOSCOW (AP) — Russian law enforcement officers on Sunday raided a hideout in the North Caucasus of armed militants allied with the Islamic State group, killing all 11 of them in an exchange of fire, the counter-terrorism agency said.

The reinforced base in a wooded, mountainous area on the outskirts of Nalchik, the capital of the Kabardino-Balkaria republic, contained a workshop for producing explosive devices and a stockpile of weapons and ammunition, the National Anti-Terrorist Committee said in a statement. It said all 11 militants were killed after opening fire on the officers and using grenades, while there were no fatalities among the officers.

An Islamic insurgency has long simmered in the predominantly Muslim North Caucasus republics of southern Russia. The region, which includes Chechnya and Dagestan, has become fertile ground for IS propaganda and recruitment, and the majority of the estimated 3,000 Russians fighting in Syria are believed to come from the North Caucasus.

The agency said the group of militants killed in Sunday’s raid were allied with IS and had helped to send local residents to Syria to fight with IS.

They also were preparing to carry out attacks in the North Caucasus, the agency said. It said two completed explosive devices were found in the hideout.

Tensions in the North Caucasus have been further heightened by Russia’s military campaign in Syria in support of President Bashar Assad in his war against the Sunni opposition. Most of Russia’s Muslims are Sunnis. Last week, Russia intensified its airstrikes in Syria in retaliation for the Oct. 31 bombing of a passenger plane in Egypt, carrying mostly Russian tourists, for which IS claimed responsibility.