BOSTON (AP) -
Two bombs exploded about 10 seconds and 100 yards apart at about 2:50 p.m. Monday in Boston's Copley Square, near the finish line of the Boston Marathon. Three people were killed, including an 8-year-old boy, and more than 140 were injured. The explosions occurred four hours into the race and two hours after the winners had crossed the finish line, but thousands of runners were still on the course.
The FBI took charge of the investigation into the bombings, serving a warrant late Monday on an apartment in the suburban Boston town of Revere and appealing for any video, audio and still images taken by marathon spectators. No arrests had been made, and authorities weren't commenting about suspects.
President Barack Obama vowed that those responsible will "feel the full weight of justice." The president was careful not to use the words "terrorism" or "terrorist attack" in his remarks, but a White House official, speaking on condition of anonymity because the investigation was still unfolding, said the attack was being treated as an act of terrorism.
The area around Copley Square remained closed Tuesday morning, as did exit ramps from major highways to the area. The Federal Aviation Administration barred low-flying aircraft within 3.5 miles of the site. Other cities also beefed up security in response to the bombing and the Secret Service expanded its security perimeter around the White House.
The FBI, U.S. Attorney's office and other law enforcement officials planned to brief the media at 9:30 a.m. Obama will be briefed Tuesday on the investigation and the ongoing response efforts from FBI Director Robert Mueller, homeland security assistant Lisa Monaco and other senior members of his team.
UPDATE: April 16 5:30 a.m.
Federal investigators say no one has claimed responsibility for the Boston Marathon attack that killed three people and wounded more than 140. But as investigators search out the who and the why, the alarm has been raised of another terror attack in the U.S. after the explosions at a public event among crowds of thousands of spectators.
UPDATE: 10:44 p.m.
Noting the tragedy of the explosions Monday at the Boston Marathon that killed three and injured more than 100, the IRS said it will be providing individual tax filing and payment extensions.
UPDATE: 10:22 p.m.
AP reports 8-year-old among the casualties, and the explosions injured at least 144 people, 17 critically.
UPDATE 8:59 p.m.
Police say at least three people have been killed in the explosions near the finish line of the Boston Marathon.
UPDATE 8:07 p.m.
Eight hospitals report that they are treating at least 130 people. Of those, at least 15 are in critical condition.
The injuries ranged from cuts and bruises to amputations. Many victims suffered lower leg injuries and shrapnel wounds. Some suffered ruptured eardrums.
Dr. Richard Wolfe, chief of the department of emergency medicine at Beth Israel Deaconess Medical Center, says one or two of the hospital's 21 patients faced a "high probability of mortality."
UPDATE 7:55 p.m.
The Navy has sent one of its bomb-disposal units to Boston to assist local authorities as needed in the aftermath of the two explosions near the Boston Marathon's finish line.
UPDATE 7:30 p.m.
Boston Police to hold news conference at 8:30 p.m. Watch it live on ABC Action News Now.
WATCH LIVE coverage at http://wfts.tv/13TPmzy.
UPDATE 7:00 p.m.
The Boston Globe reports that an eight-year-old child is one of the two fatalities.
UPDATE 6:30 p.m.
President Barack Obama, responding to the explosions at the Boston Marathon, says the United States does not know "who did this or why" but vowed that whoever is responsible "will feel the full weight of justice."
Watch the entire address in the video player above.
He said: "We will find out who did this and we will hold them accountable."
Obama made his remarks Monday evening from the White House about three hours after two explosions detonated near the marathon's finish line.
UPDATE 6:20 p.m.
ABC News is reporting at least 86 injured.
UPDATE 6:10 p.m.
UPDATE 6:04 p.m.
Google has established a person-finder for those looking for somebody, or those who have information about someone at the Boston Marathon.
UPDATE 5:52 p.m.
AP reports two people are dead and at least 57 injured after two bombs exploded near the crowded finish line of the Boston Marathon.
UPDATE 5:49 p.m.
The only nuclear power plant in Massachusetts has increased security after two bombs exploded in Boston on Monday, killing at least two people and injuring dozens. The Pilgrim Nuclear Power Station in Plymouth, Mass., about 45 miles south of Boston, was already shut down for refueling when the explosions occurred.
UPDATE 5:24 p.m.
WASHINGTON (AP) -- The Secret Service says it has expanded its security perimeter at the White House following the explosions at the Boston Marathon.
Story continues below
The White House was not on lockdown and tourists and other onlookers were still able to be in the park across the street from the executive mansion.
UPDATE 5:14 p.m.
ABC News is reporting that the JFK School of Government at Harvard University in Cambridge has been evacuated.
UPDATE 5:09 p.m.:
The NHL says Monday night's game between the Ottawa Senators and Boston Bruins at TD Garden has been postponed in the aftermath of the Boston Marathon bombings.
No makeup date has been scheduled.
The league says it "wishes to express its sympathy to all affected by the tragic events that took place in Boston earlier this afternoon."
Two bombs exploded near the finish line of the marathon on Monday, killing two people, injuring 23 others, and sending authorities rushing to aid wounded spectators. A senior U.S. intelligence official said two other explosive devices were found nearby.
UPDATE 4:57 p.m.:
A law enforcement official says cellphone service has been shut down in the Boston area to prevent any potential remote detonations of explosives.
Authorities have not identified what caused the explosives that erupted at the finish line of the Boston Marathon. The official was speaking on condition of anonymity because the investigation was ongoing.
The explosions have killed two people and injured at least 23 others.
UPDATE 4:51 p.m.
Officials report a third explosion, miles away at the JFK library. Officials are unsure if this is related to the marathon explosions.
All victims have been removed from the scene. People are recommended to stay home, and visitors should stay in their hotel rooms.
After the incident, people left shopping bags and other items. Each bag is being treated as suspicious devices and is being inspected.
Massachusetts State Police and the National Guard have been deployed
Family of victims can call 617-635-4500
If you saw anything, call 800-494-TIPS
UPDATE 4:20 p.m.
WASHINGTON (AP) -- Intelligence official: 2 more explosive devices found at Boston Marathon; being dismantled.
Boston police say two people were killed and 23 people were hurt when a pair of bombs exploded near the finish line of the Boston Marathon.
The blasts shattered the end of the race Monday, sending authorities out on the course to carry away the injured while stragglers in the 26.2-mile race were rerouted away from the smoking site.
ORIGINAL STORY 3:08pm:
Spectators and runners are describing the twin explosions that shook the finish line of the Boston Marathon today.
One woman says she was waiting for her husband to cross the finish line, and, in her words, "it just blew." She described it as "a loud boom, and then glass everywhere." Cherie Falgoust says something hit her head, and she "just ducked."
Live coverage at http://wfts.tv/13TPmzy.
A runner, Laura McLean of Toronto, says she heard two explosions outside the medical tent. She says, "There are people who are really, really bloody." McLean says, "they were pulling them into the medical tent."
The explosions took place about three hours after the winners crossed the finish line. The second one could be heard a few seconds after the first one.
A runner said, "There are a lot of people down."
Marathon workers were seen carrying one woman, who did not appear to be a runner, to the medical area as blood gushed from her leg.
You can track runners and where they were around the time of the explosions by visiting http://baa.org/individual.html.
The video below shows the moment of explosion. WARNING: May contain graphic images.