(CNN) -- Russian special forces killed five suspected militants and took another into custody Saturday during an assault on a house in the volatile Caucasus republic of Dagestan, a Russian security source told CNN.
Russia launched a search for anti-government militants in the run-up to the Winter Olympics in Sochi.
The group's alleged leader, Alexei Pashentsev, was among those killed, the source said. Pashentsev is a man of Russian ethnic origin who converted to the Islamic faith in 2010 and began contacts with militant groups, the source said.
The six suspects were in a house in the republic's capital city of Makhachkala, the source said. They were connected to the Buynaksk militant group, which had previously been linked to other militants behind bombings in late December in Volgograd in southwestern Russia, the source said.
It was not clear if any of the suspects were involved in the twin bombing attacks -- one on the city's main train station and the second, carried out within a day, on a trolley bus. In all, 34 people were killed in the attacks and approximately 100 others were wounded.
On Wednesday, state media reported that a suspected mastermind of the twin attacks was killed in a police operation in Dagestan.
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 fueled security concerns ahead of the Sochi games.
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 terrorist attacks in Russia.