At least ten people in St. Petersburg have been killed by what Russian officials are calling an “explosive device” on a city train. Details are still coming in, and so far no one has suggested who might be responsible — if indeed the first indications of an explosive device are correct:

BREAKING: St. Petersburg subway press office: Explosive device was set off on a train in the Russian city.

— The Associated Press (@AP) April 3, 2017

CNN reports that there were two explosions:

At least 10 people have been killed in twin blasts on a metro in the Russian city of St. Petersburg, state-run TASS reported.

The explosions took place on a subway car at the station.

Kremlin spokesman Dmitry Peskov said President Vladimir Putin was aware of the reports of the explosions, state-run Russia 24 reported.

Some social-media accounts are posting video in the aftermath of the explosions. This one shows significant damage to one car:

https://www.youtube.com/watch?v=7IfpJZVCieU

Fox News reports that Vladimir Putin was in St. Petersburg today, one day after organized protests in the city against his rule:

Russian news agencies quoted Kremlin spokesman Dmitry Peskov saying that Russian President Vladimir Putin has been informed about the explosion. Putin is visiting the city Monday and is expected to hold talks with the Belarusian president later in the day.

We’ll have more as developments continue. Bear in mind, however, that first reports can be inaccurate, so be sure to wait until more is known before drawing any specific conclusions.

Update: CBS reports that at least one of the devices appeared to be designed to throw off shrapnel, and that twenty or more have also been injured:

BREAKING: An explosion in a metro station
in St. Petersburg, Russia, has left several dead, state-run reports say https://t.co/sOwLJ2XsZk pic.twitter.com/2zcji7nHsM

— CBS News (@CBSNews) April 3, 2017

At least for now, it looks like a premeditated attack and not some sort of accident. If that’s the case, who had reason to conduct a terror attack on Russian transportation systems? That question has more than one answer, which is why it’s good to hold off on conclusions until more can be confirmed.

Update: Putin says he’s keeping his options open:

We are considering all causes, including terrorism – Putin: https://t.co/KuVAPZrI3d pic.twitter.com/6kyQJlsCn5

— Reuters (@Reuters) April 3, 2017

AFP reports that the St. Petersburg metro system has closed all of its stations after the explosions.

Update: CBS News now reports that two bombs went off in two different stations:

MORE: Emergency officials were quoted as saying 2 explosive devices had gone off on trains at 2 stations in Russia https://t.co/a2DdWolBQa pic.twitter.com/AskWVPMHEd

— CBS News (@CBSNews) April 3, 2017

That would explain the need to close all stations at this point. The number of wounded has now risen to over 50 in some media reports.

Update: Similar attacks took place in 2000, Malcolm Nance reminds NBC, who lists the number of suspects if this turns out to be terrorism of an external sort:

WATCH: At least one explosion hits St. Petersburg as President Putin is in the city https://t.co/k1gSXGIJhh

— NBC News (@NBCNews) April 3, 2017

Update: According to NBC’s sources, the blast(s) occurred between two stations:

An explosion tore through a subway train in the Russian city of St. Petersburg on Monday, killing and injuring an unknown number of people, officials said.

The Russian Anti-terrorist Committee told NBC News in a statement that the blast happened when the train was between two stations in the country’s second largest city. …

The blast happened when the train was between the Sennaya Ploschad and Tekhnologichesky Institute subway stations.

There may have only been one explosion, in other words, that involved two stations. Stay tuned.

Update: It could have been worse:

Russian anti-terrorism committee says it has found and deactivated a bomb at another St. Petersburg subway station. https://t.co/m9LE2TdQzT

— The Associated Press (@AP) April 3, 2017