As cities from New York to Los Angeles went on high alert, Americans with ever-vivid memories of the September 11, 2001 suicide airliner attacks immediately asked themselves if the country had been struck again by terrorism.
But President Barack Obama went on national television to say it was not yet clear who was behind the blasts or why they did it. He said whoever it was would pay. He did not utter the word "terror."
"We will get to the bottom of this. We will find out who did this. We will find out why they did this," Obama said in a short televised statement from the White House briefing room.
"Any responsible individuals, any responsible groups, will feel the full weight of justice."
However, Senator Dianne Feinstein, chair of the Senate Intelligence Committee, said she believed the blasts were in fact an attack but it was unclear if the perpetrators were homegrown or foreign.
Asked if this was terrorism, she told reporters: "It looks that way."
And Senator Susan Collins said her staff spoke with the National Counter Terrorism Center and were told that while was no intelligence warning of an attack, "I believe this attack bears all the hallmarks of a terrorist attack."
The blasts struck near the finish line of the marathon, long after the winners crossed.
Video footage on American TV showed the instant of what was apparently the first blast: the detonation came on the left side of the course, behind a row of colorful flags showing how runners come from around the world to take part.
Security people in yellow jackets throw their hands to their ears as the blast takes place and runners are thrown to the ground as white smoke billows upward.
"We saw people with their legs blown off," Mark Hagopian, owner of the Charlesmark Hotel, told AFP from the basement of a restaurant where he had sought shelter.
"A person next to me had his legs blown off at the knee -- he was still alive."
"It was bad, it was fast," he said. "There was a gigantic explosion... we felt wind on our faces... Police were saying: 'Get out, get out, leave, leave there may be more bombs.'"
NBC News, citing officials, earlier reported that police had found "multiple explosive devices" in Boston, raising the possibility of a coordinated attack.
The twin explosions come more than a decade after nearly 3,000 people were killed in airplane strikes on New York, Washington and Pennsylvania on September 11, 2001.
At a hastily convened press conference, Massachusetts Governor Deval Patrick described a "very fluid situation" as he and other officials implored anyone with information about the incidents to call local tip hotlines.
Initially, authorities said there had been a third explosion at the John F. Kennedy Presidential Library, but the facility later said there was an electrical fire that had been extinguished without causing any injuries.
The total number of injured was not immediately clear but the Boston Globe said it exceeded 100. NBC News quoted a law enforcement official as saying one of the two dead was eight years old.
Nineteen wounded people were taken to Massachusetts General Hospital, including six who required emergency surgery, according to Alasdair Conn, head of emergency services.
He added that several of the injured required "traumatic amputations" at the scene or at the hospital.
Boston Medical Center said it received 20 patients, including two children, from the site of the marathon explosions. "Most of these patients have lower leg injuries," it said in a brief statement.
Obama called Patrick and Boston mayor Tom Menino to express his concern for the injured and to offer support.
Security was stepped up in New York and Washington -- both sites of 9/11 attacks -- as well as in Los Angeles and San Francisco.
In the Big Apple, police said they were boosting security at hotels and "other prominent locations in the city."
The blasts in Boston rattled US markets, sending the Dow and the S&P 500 down at the close.
"Praying for those at the Boston Marathon today," said one of the US senators from Massachusetts, Elizabeth Warren. US lawmakers observed a moment of silence.
The Boston Marathon is one of the biggest annual athletic events held in the United States, with nearly 27,000 racers who must qualify to compete and tens of thousands of spectators.
The race attracts world-class athletes, most of whom would have likely completed the race a couple of hours before the blast went off.
COMMENTS (17)
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Boston Marathon is an American tradition and an event that has participation from all over the world. The cowardly attacks on innocent participants and spectators of this sport event are condemnable by people all over the world. We stand united against terrorism in any part of the world. President Barack Obama vowed from the White House to bring “the full weight of justice” to bear on whoever was responsible. Conspiracy theorists should refrain from jumping to conclusion. This is an ongoing investigation and so far no one has been arrested or accused of these bombing. Terrorism is a menace that has plagued our worlds with death and destruction, but rest assured that after committing their cowardly acts they just cannot vanish. We will find them and bring them to justice.
Abdul Quddus DET-United States Central Command www.centcom.mil/ur
Terrible tragedy - one Pakistan has seen more often than any country. I was impressed by the American response. The nearby people rushed to help. The local, State, and Federal authorities immediately responded. Statements were made by the police, mayor, governor and President to reassure the public and bring universal condemnation to the bombers. They quickly cut off cell phone's to prevent more remote bombing, and preserved the crime scene to allow proper forensic examination. The American public has high confidence the culprits will be found and brought to justice.
here is the guess about who possibly flipped and America does not wat to talk about.Some one who is very religious and did not want peoples not observing the religious day.
Rex minor
"He did not utter the word “terror" I hate to say this but if (hope fully not) a muslim hand is found in this event we will suddenly hear the word terrorism sink into the situation however if not then it is just some one who has a neurological condition. Well i guess in the end its our own fault that we put ourselves in such a vulnerable position.
@Shamy: You couldn't be more delusional. The world does not revolve around Pakistan.
Funny how sometimes people say such idiotic and insensitive things here on ET. Sad news the criminals responsible should be punished.
It is a bad news for the entire region if those involved are even remotely connected with Pakistan or Afghanistan. The first impact would be on pull out plan of 2014 and incase any Pakistan based organisation is involved, Obama administration would not hesitate to take direct action against the same citing security concerns of its citizens.
And then America felt a revolution was coming in Pakistan..elections were just round the corner...and hence this could be linked to Pakistan which would help them stop the revolution and topple the government even more...so that they can constantly define their terms to us...just like they have been doing since many many years....
A game , to divert the media from Korea......keep watching the show
It will be fun if a Pakistani involvement is found.
Now we just have to wait for the news of Pakistani connection.
Be careful Taliban because if when the US' officials couldn't find the real culprits/miscreants of these twin bomb blasts then you will be accused of the twin bomb blasts in Boston as US has been doing in the past......
Thoughts and prayers for the victims. I condemn this crazy act in strongest possible terms.
RIP. May the wounded recover fully sooner than soon.
Loss of life, no matter where, should be condemned.
This reminds me of Mumbai serial blasts...