By JULIE PACE Associated Press
WASHINGTON (AP) -- President Barack Obama said Tuesday the deadly Boston Marathon bombings were an act of terrorism but investigators do not know if they were carried out by an international or domestic organization, or perhaps by a "malevolent individual."
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In his second public statement in less than 24 hours since the explosions, the president said, "Clearly we are at the beginning of our investigation." He urged anyone with information relating to the events to contact authorities.
Obama said investigators "don't have a sense of motivation yet'" as they begin to evaluate the attack in which three people were killed, including an 8-year-old boy, and more than 170 were wounded.
Despite the loss of life and limb, Obama declared, "The American people refuse to be terrorized."
As he had on Monday, he said those responsible for the attacks would be brought to justice.
The president had avoided labeling the incident a terrorist attack when he stood at the same White House lectern shortly after the explosions, but lawmakers quickly said that's what it was. White House officials had said the FBI was investigating the attack as a terror incident.
Appearing before reporters on Tuesday, Obama said the events in Boston were a "heinous cowardly act, and given what we now know about what took place, the FBI is investigating it as an act of terrorism. Any time bombs are used to attack innocent civilians it is" a terrorist act, he said. Still, he cautioned that it was not known who or what organizations might have carried it out.
The president praised those who had come to the aid of the injured.
"If you want to know who we are, what America is, how we respond to evil, that's it: selflessly, compassionately, unafraid," he said.
Obama stepped to the microphone after receiving a briefing at the White House from Attorney General Eric Holder, Homeland Security Secretary Janet Napolitano and other top aides.
The bombs exploded on Monday afternoon near the finish line of the famed Boston Marathon, an annual 26 mile race through the neighborhoods of the city.
Boston's Logan Airport has heightened security the day after the two bombs exploded at the Boston Marathon.
One flight was returned to the gate and rescreened, while another was held after landing so authorities could inspect the baggage.
A US Airways spokesman says the Transportation Safety Administration asked that Flight 1716 from Philadelphia be parked remotely when it landed and the baggage inspected. Passengers were taken to a building away from the terminal during the inspection while luggage was unloaded and screened.
United Airways Flight 636 to Chicago was returned to the gate and passengers sent back through security screening at the request of the crew while the aircraft was swept. A United spokeswoman did not say why.
The TSA didn't immediately return calls seeking comment.