Russian President Dmitry Mevedev has called for tough anti-terrorism measures following a series of attacks this week.

The president said Russia must destroy those behind the attacks during a surprise visit to the southern region of Dagestan. He was in the northern Caucasus to meet security officials and leaders of the volatile republics of Dagestan, Chechnya and Ingushetia.

The visit follows Monday’s double suicide attack in Moscow’s metro, another double suicide attack in Dagestan on Wednesday in which 12 people died and the explosion of a car in Dagestan today killing two passengers.

Meanwhile in Moscow and other Russian cities, memorial services have been held for the 39 victims of Monday’s attack.

The metro attacks have been claimed by Doku Umarov, who is leader of a group of Chechen Islamic separatists calling itself the “Emirate of the Caucasus”.