MOSCOW: A female suicide bomber killed at least 16 people Sunday in an attack on the main train station of the southern Russian city of Volgograd, heightening security fears just six weeks before the Sochi Olympic Games.

Investigators said the unidentified woman set off her charge after being stopped by a police officer at the metal detectors of the central entrance to the station when it was packed with people travelling to celebrate the New Year.

Footage captured by a nearby camera showed a huge orange fireball blow out the heavy front doors and windows from the grey stone three-storey building.

Thick billows of smoke then poured out as people scattered along the rain-soaked street.

Russia's Investigative Committee spokesman Vladimir Markin said officials had launched an inquiry into a suspected “act of terror”. It was the deadliest attack in Russia in almost three years.

“A suicide bomber who was approaching a metal detector saw a law enforcement official and, after growing nervous, set off an explosive device,”Markin said in televised comments.

Doctors and police said 16 people were killed and nearly 45 injured by the explosive equivalent of more than 10 kilogrammes (16 pounds) of TNT.

Russia's interior ministry said it was immediately stepping up security at all the nation's main train stations and airports.

“These measures involve a greater police presence and more detailed passenger checks,” an interior ministry spokesman told the Interfax news agency.

The Volgograd government also introduced a heightened terror alert level in the region for the coming two weeks. The lifenews.ru website published a picture of what it said was the head of the young female bomber lying amid a pile of debris with her long brown hair spread across the floor.

The website and state-run RIA Novosti identified the bomber as a Dagestani woman named Oksana Aslanova who had been married to two different Islamists killed in battles with federal forces.

Investigators added that she may have been assisted in her attack by a man they identified only by the last name of Pavlov.

Female suicide bombers are often referred to in Russia as “black widows” -- women who seek to avenge the deaths of their family members in the fighting by targeting Russian civilians.

Olympic security fears

The city, known as Stalingrad in the Soviet era, was already attacked on October 21 by a female suicide bomber with links to Islamists.

That strike killed six people aboard a crowded bus and prompted the authorities to refocus their attention on the security measures being taken ahead of the February 7-23 Winter Games in Sochi.

The Black Sea city lies 690 kilometres (425 miles) southwest of Volgograd and in proximity to the violence in North Caucasus regions such as Dagestan and Chechnya.

Militants are seeking to impose an Islamist state throughout Russia's North Caucasus. Their leader Doku Umarov has ordered rebels to target civilians outside the region and disrupt the Games.

The Kremlin said President Vladimir Putin -- who has staked his personal reputation on Sochi's success -- was “immediately” informed of Sunday's incident and being regularly updated about the probe.

Russian authorities have repeatedly vowed to take the highest security precautions in Sochi. There have been no indications to date of foreign sports fans cancelling their attendance out of safety fears.

The UN Security Council condemned the attack “in the strongest terms”, a statement issued by its president Gerard Araud said, calling it a “heinous act”.

“Terrorism in all its forms and manifestations constitutes one of the most serious threats to international peace and security,” it said.

Acts of terrorism were “criminal and unjustifiable, regardless of their motivation, wherever, whenever and by whomsoever committed”.

Washington condemned the attack, saying it stood “in solidarity with the Russian people against terrorism of any kind”, according to a statement from the State Department.

European Union President Herman Van Rompuy in a statement also condemned “in the strongest terms the heinous attack in Volgograd”, while Nato head Anders Fogh Rasmussen said Nato and Russia “stand together in the fight against terrorism”.

EU foreign policy chief Catherine Ashton said: “There can be no excuse for such crimes. I hope that all those behind the attack will be brought swiftly to justice.”French President Francois Hollande meanwhile expressed his country's solidarity with the Russian people after the “terrible attack”.

Greece, which takes over the EU presidency in January, slammed what it called a “barbaric terrorist act.”Militant strikes have become part of daily life in the mainly Muslim North Caucasus. But the Volgograd blast will be a particular concern to the authorities as the bomber struck a city of more than one million people in the Russian heartland.