The outage was caused by equipment failure at a substation feeding into a Southern Maryland power plant, according to utility providers and US homeland security officials. There are no indications that cyber-intrusion or sabotage is responsible for the incident.
According to Joe Slater, President and CEO of Southern Maryland Electric Cooperative, which operates the powerplant in Charles County, Maryland, a Potomac Electric Power Company line feeding to their facility failed and fell to the ground.
A spokesperson for the utility company, PEPCO, said crews were on the scene investigating the failure of the PEPCO equipment. He did not confirm that the failed line fell.
The outage knocked out power during the State Department's daily briefing.
The White House experienced a power outage as well, but power came back within seconds. The West Wing is now using a back-up generator.
ABC News' Jack Date, John Parkinson, Alex Mallin, Mary Bruce and George Sanchez contributed to this report.