Britain has raised its threat level to the maximum after 29 people were injured in what police said was an unsuccessful "terrorist" bomb attack that engulfed a London Underground train in fire.
The Islamic State (IS) extremist group through its Amaq propaganda agency claimed responsibility for the September 15 attack, the fifth in Britain this year, but London's Metropolitan Police said that claim could not be verified.
Police said an "improvised explosive device" that failed to successfully detonate started a fire that engulfed a train carriage in flames during the morning rush hour at the Parsons Green subway station, and they were treating it as a "terrorist" attack.
Prime Minister Theresa May's decision to raise the threat level from "severe" to "critical" means that another attack could be imminent. She said the failed bomb was intended to cause "significant harm."
May said military personnel would take over guard duty at certain closed "protected sites," freeing up 1,000 police officers to be deployed on the transport network and on streets across Britain.
Police said the injured included burn victims and people who were trampled in a stampede. None of the victims were in serious condition, and there were no reported deaths.
London Mayor Sadiq Khan said a "manhunt" was under way to find out who was responsible, a search that police said involved hundreds of detectives backed by Britain's intelligence services.
