Female suicide bomber suspected in Volgograd bus bombing (VIDEO)

At least six people were killed and more than two dozen injured after a reported female suicide bomber detonated explosives on a public bus in the southern Russian city of Volgograd Monday afternoon.

The bomb exploded around 2 p.m. local time in a bus filled with about 40 people, according to authorities. Local police initially reported the explosion may have been due to a fuel leak in the bus, but the National Antiterrorism Committee later confirmed it was the result of a bomb.

Vladimir Markin, head of Russia’s Investigative Committee, was quoted by Russia's news agencies as saying that investigators believed the attack had been carried out by 30-year-old Naida Akhiyalova, a resident of the southern Russian republic of Dagestan.

Volgograd — a city of about 1 million people — lies on the Volga River, around 600 miles south of Moscow, and about 600 miles north of Sochi, the site of the 2014 Winter Olympics.

Several hundred miles to Volgograd's south lies the volatile and predominantly Muslim North Caucasus region, which has been plagued for years by Islamist violence. Recent targets have included local officials, security forces and non-aligned religious leaders.

Insurgent fighters there have called for an Islamic caliphate across the region. They claimed responsibility for deadly attacks in a Moscow airport in 2011 and on the Moscow subway in 2010, which killed 37 and 40 people respectively.

Investigators believe Akhiyalova was married to a member of the insurgency.

The attack, one of the largest outside the North Caucasus since the Moscow bombings, is likely to stoke further fears over security during the upcoming Olympic games. Russian President Vladimir Putin recently signed a decree placing heavy restrictions on the region surrounding Sochi starting in January.

This video, shown on Russian TV, purportedly shows the moment of the blast. It was not independently verified by GlobalPost: