At least 10 people died this morning in train car blasts in the subway system in St. Petersburg, Russia, and an unknown number of others were injured, according to state news agencies.

The two separate explosions took place at the Sennaya Ploshad station and the Technological Institute station, state news agency RIA Novosti reported.

Russian President Vladimir Putin, who is in St. Petersburg for a forum, spoke in front of cameras after the explosions, 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.”