The United States will keep its terror alert on high for mass transit as British officials try to determine the culprits and methods used in the London bus and rail bombings, Homeland Security Secretary Michael Chertoff said Sunday.

Chertoff said the code orange alert for mass transit would remain at least through Monday while the U.S. government monitors the British investigation for information about who was responsible and “what kinds of tactics we have to worry about.”

After four bombs exploded Thursday throughout the London subway and bus system, the U.S. raised its terror alert amid concern about a possible copycat attack.Full Story