MOSCOW— An Islamic militant group in Russia’s North Caucasus claimed responsibility for twin suicide bombings in the southern city of Volgograd last month and posted a video threatening to strike the 2014 Winter Olympics in Sochi.

There had been no previous claim of responsibility for the bombings, which killed 34 people and heightened security fears before next month’s Olympics.

In the video, two Russian-speaking men sitting in front of black banners with Arabic verses warned President Vladimir Putin that if the games are held, “we will give you a present for the innocent Muslim blood being spilled all around the world.”

They added that “for the tourists who come there will be a present, too.”

The video was posted Sunday on the website of the militant group Vilayat Dagestan.

An explosion in a trolleybus late December killed at least 14 people in the second suicide attack in the Russian city Volgograd in as many days, raising the specter of violence at the upcoming Winter Olympics. That attack came less than 20 hours after a bombing of a local train station that killed 17 and wounded over 30.

The attacks came several months after Chechen Islamist rebel leader Doku Umarov called for new attacks against civilian targets in Russia, including the Sochi Games.

Suicide bombings have rocked Russia for years, but most have been in the North Caucasus region, the center of an insurgency seeking an Islamist state in the region. But Volgograd, formerly known as Stalingrad, has been struck three times in two months — suggesting militants may be using the transportation hub as a renewed way of showing their reach outside their restive region.