The Secret Service says it has expanded its security perimeter at the White House following the explosions at the Boston Marathon.

Secret Service spokesman Ed Donovan says the measure was taken "out of an abundance of caution." He says it is not unusual to expand or contract the security perimeters.

Shortly after the explosions Monday, Secret Service shut down Pennsylvania Avenue outside the White House, 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.