Breaking News: Explosions at Boston Marathon

UPDATES: Boston Marathon Explosions

5:23 pm ET: Third blast later reported at JFK Library about 5 miles away, police say. Not clear whether that blast is connected to first two. (CNN)

4:58 pm ET: No one has taken responsibility for attack, says Commissioner Ed Davis.

4:48 pm ET: Massachusetts authorities confirm at least 68 patients transported to area hospitals.

4:41 pm ET: Boston Police are asking the public to turn over any video of the finish line explosion.

4:38 pm ET: “There is no sign of any radiological material involved in the explosion,” a federal source tells ABC News.

4:35 pm ET: Two more explosive devices have been found near the scene of the explosion, according to the Associated Press.

4:34 pm ET: Some 400 Massachusetts National Guard soldiers were on the scene for the marathon.

4:24 pm ET: A Federal law enforcement authority confirms to ABC News this was an intentional bombing, using small portable explosive devices.

Source: ABC News