President Barack Obama ordered his administration to do whatever is necessary to respond to and investigate blasts near the finish line Monday at the Boston Marathon, a US official said.
Obama was told of the incident, which killed two people and injured at least 23 others, shortly after it occurred and the White House has been in touch with state and local authorities.
"He directed his administration to provide whatever assistance is necessary in the investigation and response," the official said on condition of anonymity.
Officials said Obama was briefed by his top White House Homeland Security advisor Lisa Monaco and other senior aides.
The president called Boston mayor Tom Menino and Massachusetts Governor Deval Patrick to express his concern for the injured and to offer support.
Vice President Joe Biden reacted to the incident in real time, as he was on a conference call with gun reform advocates at the White House.
"As I am speaking here, they have 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."
"Our prayers are with those people in Boston who are suffering injury."
Shortly after the Boston blasts, Secret Service officers cordoned off an area adjacent to the fence at the front of the North Lawn of the White House on Pennsylvania Avenue, which would normally be thronged with crowds of tourists.