Police in Makhachkala, Dagestan, placed a district of the city under a special counter-terrorist regime on Tuesday during a search for the mastermind of a twin bomb attack on May 3, a police spokesman in the north Caucasus republic said.
A car bomb went off near a police station on the outskirts of the city on May 3 and another blast occured in a Gazelle minivan shortly afterward. The blasts killed 13 and injured at least 100.
Under Russian law, a special counter-terrorist regime allows police to introduce restrictions, including checking identities and detaining those who fail to establish who they are, and tap telephone conversations.
Dagestan remains a hotbed of Islamic insurgency, with rebels regularly carrying out attacks on law enforcements and civilians in the North Caucasus republic.