Obama: ‘We will find out who did this’

President Obama pledged Monday to bring the “full weight of justice” against those responsible for the bombing of the Boston Marathon.

“Make no mistake. We will get to the bottom of this. We will find out who did this. We will find out how they did this,” the president said in remarks from the White House. “Any responsible individuals, any responsible groups, will feel the full weight of justice.”

Obama did not use the word terrorism during his remarks, which lasted about three minutes. He ignored questions after he finished his comments.

“We still do not know who did this or why,” he said, before pledging that his administration would “monitor and respond to the situation as it unfolds.”

A White House official said the bombings were clearly terrorism.

"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. "However, we don’t yet know who carried out this attack, and a thorough investigation will have to determine whether it was planned and carried out by a terrorist group, foreign or domestic."

While saying “people shouldn't jump to conclusions,” Obama pledged to find answers.

"We don't yet have all the answers but we do know multiple people have been wounded, some gravely, in explosions," Obama said.

At least two people were killed and scores more were injured in the blasts near the finish line of the marathon, which by tradition is run on Patriots’ Day.

Eyewitness reports described bloody chaos, with twin blasts ripping through the crowd as runners finished their race.

“Michelle and I send our deepest thoughts and prayers to the families of the victims in the wake of this senseless loss,” Obama said before adding he was “supremely confident Bostonians will pull together, take care of each other and move forward – as one proud city.”

According to White House officials, the president was briefed twice through the afternoon about the bombing in Boston. The president was notified about the incident around 3 p.m. Eastern and received a first briefing from Homeland Security adviser Lisa Monaco and other members of his senior White House staff in the Oval Office.

“The president called Boston Mayor Tom Menino and Massachusetts Governor Deval Patrick to express his concern for those who were injured and to make clear that his administration is ready to provide needed support as they respond to the incident,” a White House official said.

Patrick, speaking at a press conference in Boston, said Obama had promised to assure the full cooperation of the FBI and ATF.

Later in the afternoon, the president received briefings from FBI Director Robert Mueller and Homeland Security Secretary Janet Napolitano. The White House posted a picture of Obama speaking with Mueller by phone in the Oval Office online.

House Speaker John Boehner (R-Ohio) said he and the president spoke around 5:30 p.m. Boehner planned to hold a moment of silence on the floor of the House at 6:30 p.m.

At the White House, Secret Service cordoned off Pennsylvania Avenue, moving tourists away from the gates to the executive mansion.

“Out of an abundance of caution, we have expanded our security perimeter at the White House complex,” Secret Service spokesman Ed Donovan. “It is not unusual to expand or contract these security perimeters.”