Suicide bomber kills 18 in frontline southern Russian city

At least 18 people have been killed and 40 injured in an apparent suicide bombing in the southern Russian city of Volgograd, the local authorities have said.

The blast, which ripped through the city's main railway station just after 1pm local time, is the second to strike the city in just three months, underscoring the security threat to the up coming Sochi Olympics.

By 2pm local time the regional government reported at least 18 casualties, making it the worst terrorist attack in Russia outside the restive north Caucasus since a suicide bomber killed 37 people at Moscow's Domodedovo airport in 2011.

Witnesses at the scene said that the explosion occurred near a metal detector at the entrance to the station, exploding between the front entrance and the turn-style.

The explosion just two months after another suicide bomber struck in the same Russian city will bolster fears of attacks by Islamist militants as Russia prepares to host the 2014 Winter Olympics in the Black Sea city of Sochi in less than six weeks' time.

^{Smoke billows out of the front of the station following the explosion (YOUTUBE)}

Russia's National Anti-Terrorism Committee said in a statement a female suicide bomber was to blame for Sunday's explosion.

All Russian airports and railways stations have been equipped with metal detectors and x-ray machines since the Domodedovo bombing. But the security measure means that long queues often form at the entrances as passengers wait to be searched, presenting a vulnerable target for terrorists.

The apparent bombing is the latest in a series of attacks that have underscored the on going threat from Russia's Islamist insurgency in the run up to February's Winter Olympics.

It is the second time terrorists have struck Volgograd in three months. In October a female suicide bomber blew up a bus in the city, killing seven and injuring 36.

And it comes just two days after a car bombing in the North Caucasus city of Pyatigorsk on Friday killed three people and injured two more.

Although Volgograd is several hundred kilometres from the North Caucasus republics at the the heart of Russia's Islamist insurgency, it is both more accessible target than Moscow or St Petersburg and lies outside the heavy security zone the Russian authorities have imposed around the Black Sea coast in the run up to the Olympics, making it a potentially attractive target for terrorists.

For the past several years Russian security forces have been fighting a brutal counter insurgency in the North Caucasus, where a separatist Chechen guerrilla movement has mutated into a pan-Caucasian Islamist insurgency.

Earlier this year Doku Umarov, the Chechen insurgent who heads the so-called Caucasian Emirate, issued a video message urging his followers to attack the games, which open onFebruary 7.