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A suspected mastermind of twin bomb attacks in the Russian city of Volgograd was killed in a police operation in the restive North Caucasus republic of Dagestan, state media reported Wednesday, according to CNN. 

The man died in a shootout at a house in the town of Izberbash, the official Itar-Tass news agency said.

One accomplice surrendered to police, but others were killed alongside the suspected mastermind, the news agency said.

The attacks on Volgograd's public transit system in late December, which killed 34 people and injured about 100, shocked Russia and fueled security concerns ahead of the Sochi Winter Olympics.

One bombing targeted the city's main train station and the second, carried out within 24 hours, hit a trolley bus.

Two other people were arrested last week on suspicion of transporting the suicide bombers to Volgograd.

Russian security forces have carried out a number of operations in Dagestan in recent weeks.

The southern republic is the hotbed of an ongoing Islamist insurgency blamed for previous terror attacks in Russia.