BOSTON (AP) — Two bombs exploded in the crowded streets near the finish line of the Boston Marathon on Monday, killing at least three people and injuring more than 140 in a bloody scene of shattered glass and severed limbs that raised alarms that terrorists might have struck again in the U.S.

A White House official speaking on condition of anonymity because the investigation was still unfolding said the attack was being treated as an act of terrorism.