A deadly explosion was reported on the St Petersburg Metro on Monday, April 3, killing at least nine people and injuring many others, according to the state-run TASS agency.

The blast reportedly occurred on a train between two stations, and forced the closure of the city’s metro and increased security at Pulkovo International Airport.

Russian President Vladimir Putin was in St Petersburg at the time of the attack. Speaking during a meeting with Belarus President Alexander Lukashenko, Putin sent his condolences to the families of the victims. He said all avenues were being pursued in the investigation. “We always consider all scenarios,” he said, “including accidental or criminal action, and above all, those of a terrorist nature.”