Day Two

President Obama calls Boston bombing 'act of terror' as security concerns mount

People react as an explosion goes off near the finish line of the 2013 Boston Marathon in Boston, April 15 / AP

President Barack Obama addressed the nation for the second time in 24 hours Tuesday as the investigation into the bombing of the Boston marathon ramped up.

"Anytime bombs are used to attack civilians, it is an act of terror," Obama said. It was the first time the president has used the word "terror" to describe the attack.

The dual explosions near the marathon finish line Monday afternoon, which appeared to have sprayed shrapnel, nails, and ball bearings into the crowd in a tactic reminiscent of the improvised explosive devices used by terrorists in Afghanistan and Iraq, are said to have killed three and injured 176. Among the dead is an 8-year-old boy.

Currently 103 are being treated for injuries in Boston area hospitals, with three children in critical condition, according to reports.

The Federal Bureau of Investigation Monday evening said it had assumed the lead in the inquiry to determine who is responsible for planting the devices and whether a threat remains.

The FBI is investigating the bombing as an act of terrorism, Obama confirmed Tuesday.

The identity of the individual or individuals behind the attack, whether such persons are domestic or international, and whether the individual or individuals operated as lone wolfs or wolves or as part of a terrorist organization remained unknown, the president said.

Obama repeated his commitment of the full resources of the federal government to the investigation.

"The American people refuse to be terrorized," he said.

No additional explosive devices have been found, authorities said Tuesday morning.

The first successful act of terrorism on U.S. soil since Sept. 11, 2001, the bombing heightened security concerns throughout the country.

A plane in Boston's Logan Airport was reported to have been evacuated due a security concern Tuesday morning. One of the terminals at La Guardia Airport was also evacuated briefly but was soon pronounced clear.

"If you see something suspicious, speak up," the president said during his brief statement.