Boston officials on marathon blasts

NBC News reported that a small home-made bomb is the preliminary cause of the explosions. President Obama was informed of the explosions at 3:49 p.m.

"The President has been notified of the incident in Boston," a White House official said in a statement. "His administration is in contact with state and local authorities. He directed his administration to provide whatever assistance is necessary in the investigation and response."

For more on the blasts, click here.