Defense Secretary Chuck Hagel is calling the Boston marathon bombing that killed three and wounded more than 140 people a "cruel act of terror."
Hagel said Tuesday that any event with explosive devices is clearly an act of terror and promised that a thorough investigation will determine whether the perpetrators were foreign or domestic.
He said government officials still do not know who is responsible or why the historic race was targeted Monday.
The Pentagon chief vowed that those responsible will be brought to justice.
Hagel made the comments Tuesday at the start of a previously scheduled congressional hearing on the defense budget.
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