London's Metropolitan Police say an "improvised explosive device" started a fire on a London Underground train in a "terrorist" attack that injured 22 people.
Police said the injured on September 15 included burn victims and people who were trampled in a stampede.
None of the 22 hospitalized victims were in serious condition, and there were no reported deaths.
The attack occurred on a packed train during the busy morning rush hour at Parsons Green station, an aboveground station in southwest London on the Wimbledon branch of the subway system's District Line.
Initial British media reports said a white container "exploded" on the train, but police said later that the explosive device did not fully detonate.
One witness told Reuters he was on the train at Parsons Green when he heard a "whoosh" and saw the next car become engulfed in flames.
Armed police were on the scene while ambulance crews were treating the injured.
Prime Minister Teresa May said she would chair a meeting of the National Security Council later on September 15.