An “improvised explosive device” was detonated on a Tube train in south-west London during Friday’s rush hour, Scotland Yard has confirmed.
Assistant Commissioner Mark Rowley said hundreds of detectives, working with MI5, are investigating the blast at 08:20 BST at Parsons Green station.
Eighteeen people have been taken to hospital mostly with burn injuries.
The blast, on an eastbound District Line train from Wimbledon, is being treated as terrorism, police said.
The Metropolitan Police said it was too early to confirm the cause of the fire and the station, which is above ground, has been cordoned off.
Pictures show a white bucket on fire inside a supermarket bag, with wires trailing on to the carriage floor.
