Obama Calls Boston Bombings an 'Act of Terror'

President Barack Obama called the Boston bombings an "act of terror'' on Tuesday, but said it is not clear yet whether the twin blasts were the work of a foreign or domestic group or a "malevolent individual.''

In an appearance in the White House briefing room, Obama urged Americans to be vigilant and to watch for suspicious activity a day after two explosions rocked the finish line of the Boston Marathon, killing at least three people and wounding scores more.