The two bomb blasts in Boston, that killed at least three people besides leaving over 130 injured, are being approached as a terrorist attack by the US authorities, a White House official has said.
"Any event with multiple explosive devices, as this appears to be, is clearly an act of terror, and will be approached as an act of terror," the official said on condition of anonymity, as he was not authorised to speak to the press.
"However, we don't yet know who carried out the attack and a thorough investigation will have to determine whether it was planned and carried out by a terrorist group, foreign or domestic," he added.
President Barack Obama, however, did not say anything on whether the blasts were an act of terror.
"We still do not know who did this or why. And people shouldn't jump to conclusions before we have all the facts. But make no mistake, we will get to the bottom of this," Obama said.
While Obama refrained from declaring it as a terrorist attack, several lawmakers were quick to pronounce it that way.
"My understanding is that it's a terrorist incident," Senator Dianne Feinstein, Chairperson of the Senate Intelligence Committee told reporters.
"In my judgement, this has all the hallmarks of an act of terrorism, but we do not know for sure who did it," the House Homeland Security Committee Chairman Michael McCaul said.
"I am in touch with local authorities in Boston as well as federal authorities who have launched an investigation into this malicious attack and I am certain that whoever is responsible will be held accountable," said McCaul.
"My sympathies go out to victims of the terrorist attack in Boston as well as to their families. Though it remains unclear who is responsible, this attack is yet another stark reminder that we must remain vigilant in the face of continuing terrorist threats," said Ed Royce, Chairman of the House Foreign Affairs Committee.
The House Democratic Whip Steny H Hoyer also termed the blasts as an act of terror.
"As the evidence mounts that this was a terrorist attack, our intelligence and law enforcement agencies must do whatever is necessary to find and interrogate those responsible so we can prevent similar attacks," said Senator Saxby Chambliss, Vice Chairman of the US Senate Select Committee on Intelligence.
Senators Susan Collins, and Angus King said "initial news reports that multiple improvised explosive devices may have been involved at this high-profile national event bear the hallmarks of a terrorist attack."
Both are members of the Senate Select Committee on Intelligence.
The last two major terrorist attacks on US soil were claimed by the outfits within 72 hours.
The 2010 Times Square attack by Tehrik-i Taliban Pakistan (TTP) was claimed in less then 24 hours in a video while the Christmas Delta attack occurred in 2009 by Al-Qaeda in the Arabian Peninsula (AQAP) was claimed in 72 hours in a written statement.
Experts said the claim of responsibility for this attack could be delivered in video, written or audio form and may be distributed broadly or direct to the media.
The current location of the attacker(s) and the overall plan, if involving follow-on attacks, may impact the timing of a claim.
