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Home-grown terrorists may be behind yesterday's twin explosions that ripped through the cheering crowd at the finish line of the popular Boston Marathon, killing at least three people and injuring over 140.
President Barack Obama, who said any "responsible groups will feel the full weight of justice" did not call the explosions an act of terror but a little later a White House official said they were approaching the blasts as an act of terror.
Some terrorism experts warned that it will be "fool hardy" to speculate but other analysts believe that it was unlikely that an international terror network was behind the explosions.
Early reports suggest that the devices were crudely made otherwise, they probably would have killed many more people making it unlikely that they were the work of a foreign government or global terrorist group, such as alQaeda, the experts were quoted as saying by Boston Globe.
But the Boston Marathon is an unusually public event, giving hundreds of thousands of people easy access to the 26-mile route, and the bombs could have been set off by radical Islamists from the United States influenced by events or clerics in the Middle East, local extremists on either the left or right, or deranged killers with no ideological agenda.
Radical Muslims "will be everyone's favourite suspect, but there are many other possibilities," said Brian Michael Jenkins, a terrorism specialist at the Rand Corp.
Some media outlets reported a Middle Eastern connection in the Marathon bombing, too, saying that authorities were questioning a Saudi national being treated for burns at an area hospital.
But Boston police said they have made no arrests, and the FBI issued a statement saying it "remains too early to establish the cause and motivation" of the attack, though the FBI agent overseeing the Boston office, Richard DesLauriers, called it a "potential terrorist investigation".
Terrorism experts point out that domestic terrorists have been behind other attacks on US soil, including the Oklahoma City bombing that killed 168 people in 1995, the deadly Olympic Park bombing in Atlanta in 1996, and the Unabomber, who killed three people in more than a dozen attacks from 1978 to 1995, the report said.
The two blasts occurred within seconds on a sidewalk along the 42-kilometre route of the Boston Marathon, where thousands of people had lined up to cheer on the marathoners yesterday.
Hospitals reported at least 144 people are being treated,with at least 17 of them in critical condition and 25 in serious condition. At least eight of the patients are children.
Media reports quoted law enforcement sources as saying that the dead included an 8-year-old boy.
The authorities also found two devices at two other locations in the city, but they did not explode.
Several mega cities in the US, including New York, Los Angeles, Chicago and Washington, have been put on alert.
FBI special agent in charge Richard DesLauriers told reporters here that the investigation into the blasts is an "ongoing and criminal investigation that is a potential terrorist investigation."
Media reports quoted a law enforcement advisory as saying that investigators have warned police to be on the lookout for a "darker-skinned or black male" with a possible foreign accent in connection with the attack.
The man was seen with a black backpack and sweatshirt and was trying to get into a restricted area about five minutes before the first explosion near the finish line of the annual Boston marathon yesterday afternoon, CNN said.
President Obama was briefed on the explosions by Homeland Security adviser Lisa Monaco.
Obama said those responsible are yet to be identified, and cautioned that "people should not jump to conclusions before we have all the facts."But make no mistake, we will get to the bottom of this. And we will find out who did this and we'll find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice," Obama said.
The two blasts created chaos and havoc as runners and spectators scrambled to escape the venue. Blood and debris was strewn on the sidewalks near the finish line of the marathon.
The blasts occurred in the heart of Boston city, an area dotted with popular tourist destinations, bars, luxury shops, restaurants and busy hotels.
The bomb was apparently placed in a garbage can and exploded just as the last of the nearly 27,000 marathoners were approaching the finish line.
The marathon is held annually on the Patriots' Day, the third Monday of April, a state holiday in Massachusetts.
The blasts occurred as thousands of spectators lined the sidewalks to cheer on the marathoners.
