According to the Associated Press, Boston-area hospitals reported at least 144 people injured and three dead. At least 17 of the wounded are classified in critical condition; doctors described performing multiple amputations and removing dozens of bits of shrapnel from victims.

The FBI and Massachusetts officials said Monday night that the area surrounding the marathon finish line was being secured as a crime scene by members of the National Guard. Access to the area remained restricted on Tuesday morning.

"We will go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime, and we will do everything we can to bring them to justice," said Richard DesLauriers, FBI agent in charge.