(ABC News)--At least nine people died this morning in a train car blast between two subway stations in St. Petersburg, Russia, state news agencies said.

An explosive device was later discovered and disarmed at a different metro station, according to Russian state media and The Associated Press.

State news agency RIA Novosti had said today that two separate explosions took place at the Sennaya Ploshad station and the Technological Institute station, but The Associated Press has since reported that one unidentified explosive device went off on a train traveling between the two stations.

State news agency TASS also reported that there was only one blast between the two stations.

Russia’s National Antiterror Committee says preliminary information suggests that at least nine people were killed and at least 20 people were injured, some seriously, according to Russian news agency Interfax. A spokesman for St. Petersburg's governor had said earlier that at least 10 people were dead.

Russian President Vladimir Putin, who is in St. Petersburg for a forum, spoke in front of cameras after the explosion, alongside the president of Belarus, Aleksander Lukashenko.

“Unfortunately, we have to begin our meeting with this tragic event,” Putin said. “The causes are not yet clear, and so it’s still early to talk about that, the investigation will show. But, naturally, we always examine all versions, ordinary and criminal, above all incidents of a terrorist character.”

Later, Russia's National Antiterrorism Committee said an explosive device was discovered and disarmed in a different metro station in St. Petersburg, Ploshad Vostaniya, according to Russian state media and the AP.

Pictures of thick clouds of smoke at the metro station circulated online shortly, as well as what appeared to be a mangled train car.

Passengers appeared to be fleeing the smoke-filled station.

Metro service in St. Petersburg has been shut down, according to the city's press office.