BOSTON: The twin explosions near the finish line of the Boston Marathon Monday killed two people and wounded more than 100, officials and media outlets said.
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.
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