Secret Service expands security at White House after Boston explosion

The Secret Service expanded its security perimeter at the White House on Monday following the explosions at the Boston Marathon.

Secret Service spokesman Ed Donovan said the measure was taken "out of an abundance of caution" and noted that it was not unusual to expand or contract the security perimeters.

President Obama was briefed on the explosions by FBI Director Robert Mueller and Homeland Security Secretary Janet Napolitano. The White House said the president also spoke with Massachusetts Gov. Deval Patrick and Boston Mayor Tom Menino and pledged to provide whatever federal support was needed in responding to the incident.

Vice President Joe Biden was on a conference call with gun control activists when staffers turned on televisions in his office Monday to view coverage of the explosions. He said during the call that his prayers were with those in Boston.

The Secret Service, as part of its expanded security near the White House, shut down Pennsylvania Avenue, cordoning off the area with yellow police tape. Several Secret Service patrol cars also blocked off the entry points to the road.

The White House was not on lockdown and tourists and other onlookers were still able to be in the park across the street from the executive mansion.