At least 29 people were injured when a makeshift explosive device blew up in the London stain system during Friday morning's rush hour. No life-threatening injuries have been reported and eight of those injured have been treated and sent home.
British Prime Minister Theresa May told the nation the danger may not be over.
"The Joint Terrorism Analysis Center that's the independent organization which is responsible for setting the threat level on the basis of available intelligence has now decided to raise the national threat level from severe to critical. This means their assessment is that a further attack may be imminent."