Boston Marathon Bombing, Getty Images
Aamer Madhani and Paul Singer, USA TODAY
President Obama vowed Monday night to get to the bottom of who is behind a pair of deadly explosions near the finish line of the Boston Marathon, but he warned Americans not to jump to any conclusions.
"We still do not know who did this, or why, and people shouldn't jump to conclusions before we have all the facts," Obama said in a brief statement to reporters hours after the deadly explosions at the iconic American sporting event. "But make no mistake, we will get to the bottom of this."
He added: "We will find out who did this. We'll find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice."
While Obama cautioned against jumping to conclusions about the motive for the explosions, a senior administration official said the incident was "clearly an act of terror and will be approached as an act of terror."
"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," said the official, who was not authorized to speak publicly and spoke on the condition of anonymity.
Obama was notified about the blasts at about 3 p.m., and administration officials have been coordinating with Massachusetts and Boston authorities since.
Obama spoke with Boston Mayor Tom Menino and Massachusetts Gov. Deval Patrick and told them that he was ready to offer Boston any support needed to respond to the incident. Obama was briefed by FBI Director Robert Mueller and Department of Homeland Security Secretary Janet Napolitano on the investigation and response to the incident in Boston. The president also spoke to House Speaker John Boehner and Senate Minority Leader Mitch McConnell.
Boehner ordered American flags to be lowered outside the U.S. Capitol to half-staff Monday evening.
"Words cannot begin to express our sorrow for the families who are grieving so suddenly right now," Boehner said. "The House of Representatives offers its prayers to the victims and the city of Boston. We also give thanks for the professionals and Good Samaritans who prevented further loss of life. This is a terrible day for all Americans, but we will carry on in the American spirit and come together with grace and strength."
On the Senate floor, Majority Leader Harry Reid held a moment of silence shortly after 5:30 p.m. And the president called on Americans to keep the city of Boston in its thoughts.
"The American people will say a prayer for Boston tonight," Obama said
Vice President Biden appeared to have learned of the explosions in Boston from television.
MORE: Full coverage of explosions at Boston Marathon
During a call with gun-control activists Monday afternoon unrelated to the incident, Biden said, "As I am speaking here, they just turned on the television in my office and apparently there has been a bombing - I don't know any of the details of what caused it, who did it."
Biden added, "Our prayers are with the people in Boston who have suffered injury. And I don't know how many of them there are."
Not long after the explosions in Boston, authorities in Washington closed off an area near the White House to pedestrian traffic.
"Out of an abundance of caution, we have expanded our security perimeter at the White House complex," said U.S. Secret Service spokesman Edwin Donovan. "It is not unusual to expand or contract these security perimeters."
Washington Mayor Vincent Gray also said that commuters would see a stepped-up police presence Monday night.
Politicians from New England and throughout the country responded with a mixture of heartbreak and outrage:
"Our thoughts and prayers are with the victims, and our heartfelt thanks go out to those first responders, medical personnel, volunteers and citizens who were on the scene to help those in need," said Sen. Jack Reed, D-R.I. "I have faith that law enforcement will get to the bottom of this and hold whoever is responsible accountable to the fullest extent."
"Our hearts are heavy with the news out of Boston today. #PrayforBoston," tweeted the 2012 GOP presidential nominee and former Massachusetts governor Mitt Romney.
"Heartbreaking day for Boston. Praying for everyone back home as this terrible tragedy unfolds," tweeted Rep. Joe Kennedy, D-Mass.
In another tweet, Rep. Eric Swalwell, D-Calif., said he was praying "for those murdered."
Within hours of the incident, the five candidates running in the special Senate election in Massachusetts announced they were suspending their campaign activities out of respect to the victims.