White House officials say the attack is being treated as an \'act of terror\' At least two people were killed and three dozen wounded when two explosions struck near the finish line of the Boston Marathon on Monday, sparking scenes of panic. Police did not immediately say whether the explosions were part of a terrorist attack, but marathon organizers said it was a twin bombing and media outlets reported that other unexploded devices had been found nearby.
The blasts left a street littered with blood and debris, as spectators screamed and fled, paramedics hauled away stretchers and police rushed in, according to witnesses, one of whom saw a man with his lower limbs blown off.
Boston Marathon organizers said on Facebook that \"two bombs\" exploded near the finish line, without providing a source for the information.
\"We are working with law enforcement to understand what exactly has happened,\" it said.
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.
Boston Police Chief Ed Davis said there was a third explosion at the John F. Kennedy Presidential Library, but the library later said there was an electrical fire that had been extinguished without causing any injuries.
Meanwhile, British race organisers said the London Marathon would go ahead on Sunday despite the Boston attacks, but police said they would review security plans.
British Prime Minister David Cameron wrote on Twitter that footage from the blasts was \"shocking and horrific\", and said that his thoughts were with those affected.
While it has yet to be confirmed whether the explosions on Monday were caused by a terror attack, the shocking scenes quickly prompted fears of a similar incident at the London race.
\"We will not be cancelling, what we are doing, we are reviewing,\" London Marathon Chief Executive Nick Bitel told BBC Radio 5 Live.
\"You look at what has occurred, if there are steps we can take to increase security and all sorts of measures one could deploy.
\"We run through the city, when you have an event of any nature, a marathon, parade, it\'s only as safe as the city itself, if it\'s not held in a stadium you can\'t do a lockdown like you may do in a building,\" he added.
Thousands of people, including leading international athletes, compete in the London Marathon every year and, with the race just six days away, there was earlier speculation the event could be cancelled on safety grounds.
Bitel said he was \"deeply saddened and shocked by the news.
\"Our immediate thoughts are with the people there and their families,\" he said in a statement. \"It is a very sad day for athletics and for our friends and colleagues in marathon running.
\"Our security plan is developed jointly with the Metropolitan Police and we were in contact with them as soon as we heard the news.\"
Met Police Chief Superintendent Julia Pendry added: \"A security plan is in place for the London Marathon. We will be reviewing our security arrangements in partnership with London Marathon.\"
The explosions in Boston took place after the elite race had finished.
Lelisa Desisa of Ethiopa won the men\'s race with Rita Jeptoo winning the women\'s event.
British Foreign Secretary William Hague said he was \"appalled by news\" while Irish Prime Minister Enda Kenny offered his sympathy to the people of Boston, a city with strong Irish roots.
\"On behalf of the Irish people, I am sending our sympathy and support to Mayor Menino and Governor Patrick and to the people of Boston who have been devastated by this senseless and terrible event,\" he said.
\"Our thoughts and prayers are with the victims and their families.\"
Paula Radcliffe, the British women\'s marathon world record holder, said she was \"horrified to hear news\".
\"Really hope there are no serious casualties. Situation looks awful, thoughts with everyone. There are some very sick people out there, who would do something like this?\"
Competitor Abi Griffiths, one of more than 370 British athletes officially competing in the event, completed the race 10 minutes before the explosions and explained that it was immediately clear something was wrong.
\"There is a protocol when you finish a marathon -- first of all you just want to fall on your hands and knees because it is just so exhausting,\" she told Sky News.
\"It was while I was getting my bag that I heard it go off.
\"The ground shook and immediately people sort of looked around -- it was just too loud to be something that wasn\'t serious.\"
The Boston race, the world\'s oldest annual Marathon, is held each year on the United States\' Patriots\' Day.