Deadly blast hits St Petersburg metro

Ten people have been killed in an explosion between two
underground stations in St Petersburg.

The head of Russia's National Anti-Terrorist Committee said the
blast hit a train between Sennaya Ploshchad and
Tekhnologichesky Institut stations.

The committee said an explosive device was later found and
made safe at another station nearby.

President Vladimir Putin said all causes, especially terrorism, were
being investigated.

What happened?

The first images posted on social media showed a train at a
platform in Tekhnologichesky Institut station with a hole blown in
its side, along with a number of casualties.

Initial reports suggested there had been two explosions, one each
at Sennaya Ploshchad and Tekhnologichesky Institut stations.
But the Russian National Anti-Terrorist Committee later confirmed
there had been only one explosion between the two stations, at
about 14:40 local time (11:40 GMT).

Senior investigator Svetlana Petrenko told Russian media the train
driver's decision to continue to the next station almost certainly
helped save lives, as it allowed people to be rescued quickly.

The number of casualties given by officials has differed
throughout the day. In the most recent update, Health Minister
Veronika Skvortsova said 10 people had died - seven at the
scene, one in an ambulance and two in hospital - and that 37
people were hurt.

The entire St Petersburg underground network has now been shut
down, and metro officials in the capital Moscow said they were
introducing extra security measures there as a result.

What was the cause?

Andrei Przhezdomsky, the head of the National Anti-Terrorist
Committee, said the explosion was caused by "an unidentified
explosive device" but that the exact cause had yet to be
determined.

President Putin was in St Petersburg at the time of the blast, his
spokesman Dmitry Peskov said.

"I have already spoken to the head of our special services, they
are working to ascertain the cause," Mr Putin said, at a meeting
with Belarus President Alexander Lukashenko.

The discovery of an explosive device at another station,
Ploshchad Vosstaniya, indicates the attack was deliberate, and
reports in Russia say the explosion came from a briefcase left on
the train.

Is this unprecedented?

St Petersburg's metro system is the 19th busiest in the world,
with more than two million passengers every day, but it has not
suffered attacks before.

Several transport hubs in Russia have, however, been attacked. In
2010, 38 people died in a double suicide bombing on the
Moscow metro.

And a year later, a bomb exploded on a high-speed train
travelling between Moscow and St Petersburg, killing 27 and
injuring another 130.

Both attacks were claimed by Islamist groups.