Reports claim Russia explosion was caused by bomb filled with shrapnel

SAINT PETERSBURG, Russia - At least 10 people were killed and 50 injured when an explosion tore through a train carriage in the Saint Petersburg underground system on Monday, Russian authorities said.

Interfax news agency quoted an unnamed source as saying the blast was caused by a bomb filled with shrapnel.

"The Saint Petersburg prosecutor's office has begun to investigate the blast in a train carriage" at the Technological Institute metro station's platform, a prosecutors' statement said.

A source in the emergencies services told Russian news agencies that "around ten people were killed", according to preliminary information.

Video showed injured people lying bleeding on a platform, some being treated by emergency services and fellow passengers. Others ran away from the platform amid clouds of smoke, some screaming or holding their hands to their faces.

A huge hole was blasted in the side of a carriage with metal wreckage strewn across the platform. Passengers were seen hammering at the windows of one closed carriage.

The station is a busy hub of the underground network in the center of Russia's second largest city.

The Saint Petersburg metro said in a statement carried by Russian news agencies that it had closed two stations, Technological Institute and Sennaya Ploshchad - two neighboring stations on one line - and was evacuating passengers.

"Evacuation of passengers is ongoing, there are people injured," it said. "An unidentified object supposedly blew up in a (train) carriage."

President Vladimir Putin, who was holding a meeting with Belarus President Alexander Lukashenko near Saint Petersburg in his official Strelna presidential palace, offered "condolences" to those hurt in the blast.

He added that the government was considering all possible causes for the blasts, including terrorism.

"I have already spoken to the head of our special services, they are working to ascertain the cause (of the blasts)," Putin said.

"The causes are not clear, it's too early. We will look at all possible causes, terrorism as well as common crime."

Following the reports, the Moscow metro also announced that it was "taking additional security measures" as required by law in such situations, according to the network's official Twitter account.

While there was no immediate indication as to what caused the blast, Russia's security services have previously said they had foiled "terrorist attacks" on Moscow's public transport system by militants, some of whom were trained by Islamic State jihadists in Syria.

And Russia's public transportation systems have been targeted by attacks in the past.

In 2013, Russia was hit by twin suicide strikes that claimed 34 lives and raised alarm over security at the Sochi Winter Olympic Games.

A bombing at the main railway station of the southern city of Volgograd killed 18 people on while a second strike hit a trolley bus and claimed 16 lives.

A suicide raid on Moscow's Domodedovo airport that was claimed by Islamic insurgents from the North Caucasus killed 37 people in January 2011.

AFP-Reuters-AP