D.C. authorities say they are increasing security after a pair of explosions rocked the Boston Marathon.

Police spokeswoman Gwendolyn Crump said the District had "heightened security," and Metro said the transit agency had "ordered all day-shift patrol officers to remain on duty through this evening's rush hour to increase the security posture of the transit system."

Metro said there was not a "specific or credible" threat against the rail and bus system. The White House closed Pennsylvania Avenue to pedestrians and ordered onlookers across the street to Lafayette Park.