REPUBLIKA.CO.ID, MAKHACHKALA -- Russian security forces said on Wednesday they had killed a militant who may have masterminded suicide bombings that killed 34 people in the southern city of Volgograd in December and raised fears for the security of the Sochi Olympics.

Dzamaltin Mirzayev was killed in a shootout with by law enforcement officers who surrounded a home in the North Caucasus province of Dagestan, a spokesman for regional investigators said.

Authorities believe Mirzayev may have sent two men from Dagestan to carry out the bombings at a train station and on a trolleybus in Volgograd on Dec. 29 and 30, he said.

The bombings raised concerns of further attacks by Islamist militants based in the North Caucasus before or during the Sochi Winter Olympics, which open on Friday.

Dagestan, on the Caspian Sea about 570 km (350 miles)southeast of Sochi, is beset by near-daily violence linked to the insurgency.

Russian authorities said last week they had identified the bombers and arrested two men suspected of helping send them to Volgograd from Dagestan.

An official at the National Anti-Terrorism Committee, which made last week's announcement, declined to comment on whether Mirzayev was linked to the Volgograd bombings.

In a video clip posted on the Internet in July, the leader of the North Caucasus insurgency urged fighters to do all they could to prevent the Olympics going ahead.

The head of security for the Olympics, a prestige project for President Vladimir Putin, said last week that there was no "concrete threat" to those attending the Games.

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