Boston Marathon Explosions: Three Dead

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The FBI is leading a terror investigation after three people were killed and more than 140 others hurt in a twin-bombing attack during the Boston Marathon. Spectators' cheers turned to screams as the explosions ripped through the crowd near the finish line, causing horrific injuries.

An eight-year-old boy is among the dead.

The blasts happened within seconds of each other and about 100m (330ft) apart, blowing out windows and sending smoke and debris into the air. Emergency workers tore down fencing and carried away seriously injured men and women amid scenes of panic and confusion in the heart of the city.

Of the 144 reported injured, 17 are in a critical condition. Massachusetts General Hospital said "several amputations" were performed on survivors. Others had limbs torn off by blast forces. More than 25,000 people were registered as taking part in the race, 374 of whom were British. There were also 108 Irish athletes.

There have been no immediate claims of responsibility for the attack, the most serious in the US since the 9/11 World Trade Centre atrocity. Al Qaeda-linked groups and militant white extremists have attacked targets in America in the past. The Pakistani Taliban, who have previously threatened attacks in the US, have denied any involvement.

Barack Obama vowed to find and punish those responsible, as a senior White House official said the attacks were being treated as an act of terrorism. Mr Obama said officials "still do not know who did this or why".

But he vowed: "We will find out who did this. We'll find out why they did this. Any responsible individuals, any responsible groups, will feel the full weight of justice."

Bill Bratton, a former head of Boston police who is now based in London, said: "Unfortunately in my country there are no shortage of potential suspects, if you will."

The marathon is held every year on Patriots' Day, a Massachusetts state holiday which commemorates the first battles of the American Revolution in 1775. The explosions happened on Boylston Street, four hours into the race and about two hours after the men's winner had crossed the line, as amateur runners were reaching the finish.

More than 17,000 competitors had completed the race by the time the blasts struck. TV helicopter footage showed blood on the ground and the desperate efforts of rescuers in the popular shopping and tourist area known as the Back Bay. A woman near the second bomb, Brighid Wall, 35, said people had frozen, unsure of what to do.

Her husband threw their children to the ground, lay on top of them and another man lay on top of them and said: "Don't get up, don't get up."

She said she saw six to eight people bleeding profusely, including one man who was kneeling, dazed and bleeding from his head. Another person was on the ground covered in blood and not moving.

"My ears are zinging", she said. "Their ears are zinging. It was so forceful. It knocked us to the ground."

Bill Iffrig, a runner who was filmed falling to the ground as the first blast went off, said "the shockwave must have hit me. My legs felt like noodles". He was able to walk away and speak to reporters at the scene.

Runner Tim Davey, from Virginia, was with his wife Lisa and their children in a medical tent set up for exhausted runners. "They just started bringing people in with no limbs," he said.

Roupen Bastajian, 35, a state police officer from Rhode Island, had just finished the race when he heard the blasts.

"There were people all over the floor," he said. "We started grabbing tourniquets and started tying legs.

"A lot of people amputated ... At least 25 to 30 people have at least one leg missing, or an ankle missing, or two legs missing."

One British runner, Anthony Meenaghan, said he was "safe and well" but added: "Can't believe what I saw and heard".

Mr Meenaghan, 21, is an architectural technology student from Sheffield Hallam University who is on a work placement in Boston. He was running with his father, who is also called Anthony.

He tweeted: "Thanks for all messages. I'm safe and well. Can't believe what I saw and heard. Sad day."

A senior US intelligence official said another two unexploded bombs were found and disarmed near the end of the 26.2mile (42km) route. There were reports of a third blast at the JFK library a few miles away but that was later confirmed as a fire that was believed to be unrelated to the blasts. No one has been arrested, although officers searched an apartment in the Boston suburb of Revere as part of the investigation.

A no-fly zone was also put in place over the city as security was tightened and flights bound for Boston's Logan International Airport were briefly held up at other airports. Boston Police Commissioner Edward Davis said the authorities had received "no specific intelligence that anything was going to happen".

At Massachusetts General Hospital, Alisdair Conn, chief of emergency services, said: "This is something I've never seen in my 25 years here ... this amount of carnage in the civilian population. This is what we expect from war."

Police and doctors quoted by US media said ball bearings had been packed into the injuries, causing horrific injuries.