A senior U.S. intelligence official says two more explosive devices have been found near the scene of the Boston marathon where two bombs detonated earlier.
The official said the new devices were being dismantled.
It was not immediately clear what kind of devices had been found Monday. The official said the first two did appear to be bombs.
The official spoke on condition of anonymity because he was not authorized to discuss the findings publicly.
The official said it was not clear what the motive was or who may have launched the attack.