A female suicide bomber set off a blast that killed at least six people on a bus Monday in the Russian city of Volgograd, just hours north of the resort town of Sochi, where Russia will host the 2014 Winter Olympics.
The explosion injured more than 30 people, many of them critically.
A witness who was driving behind the bus told Rossiya-24 television: “There was a blast — a bang — all the glass flew out of the windows. The cloud of smoke quickly dissipated and then I saw people start to fall out and run out to escape the bus. It was a horrible sight.”
The attack is the deadliest in the North Caucasus region in the last three years. Boston Marathon bomber Tamerlan Tsarnev was born in the North Caucasus in 1986.
The region is plagued by Islamist insurgents from Chechnya, a Russian state that has been fighting for independent since 1921.
Russian President Vladimir Putin ordered more security in the region, after he staked his reputation on the February games.
Volgograd is about 600 miles north of the city of Sochi, which sits on the Black Sea.
“Today at 2:05 pm, an unknown explosive device detonated on a passenger bus in the city of Volgograd, causing human casualties,” said Russia’s national anti-terrorism committee.
The bomber is believed to be a “black widow” of an Islamist militant.
“According to preliminary information, the self-explosion was carried out by a 30-year-old Dagestani native, Naida Akhiyalova,” said Investigative Committee member Vladimir Markin.
Dagestan is also a federal subject of Russia.
Her identity was confirmed by one of the passengers who survived the blast. Investigators believe there were about 40 people on board.
There was no immediate claim of responsibly from any terror group.
“A criminal case has been opened under articles outlining terrorism, murder and the illegal use of firearms,” Markin told RIA Novosti news agency.
Insurgents were responsible for a 2011 suicide bombing that killed 37 at a Moscow airport, and two back-to-back bombings that killed 40 in the Moscow subway in 2010.