Russia's counter-terrorism agency says security forces in Dagestan have killed three militants who had sworn allegiance to the Islamic State group, including one who had returned from Syria this year.

Police say nearly a third of the estimated 3,000 Russians who have gone to fight alongside IS militants in Syria are from Dagestan, a predominantly Muslim republic in southern Russia where an Islamic insurgency has simmered for years.

The National Anti-Terrorist Committee announced Sunday that security forces had killed the three militants after they refused to surrender.

President Vladimir Putin said one of the goals of Russia's air campaign in Syria was to prevent Russians fighting with IS from coming back. Most are deterred from returning by the knowledge that they would likely be killed or face long prison terms.