29 injured in blast on London subway
LONDON — A homemade bomb planted in a rush-hour subway car exploded in London on Friday, injuring 29 people and prompting authorities to raise Britain’s terrorism threat level to “critical,” meaning another attack may be imminent.

The early morning blast sparked a huge manhunt for the perpetrators of what police said was the fourth terrorist attack in the British capital this year.

Prime Minister Theresa May, acting on the recommendation of the Joint Terrorism Analysis Center, raised the country’s threat level from “severe” to “critical” — its highest possible level. Ms. May said military troops would augment the police presence in a “proportionate and sensible step.”

Earlier, Ms. May said the device had been “intended to cause significant harm.”