The U.S. Homeland Security Department said there is "no indication" widespread power outages Tuesday in Washington and its suburbs were linked to "malicious activity."
The outages affecting the White House, State Department and other sites were quickly attributed to an explosion at a power plant in the neighboring state of Maryland.
Electricity provider Pepco said on Twitter it was working to repair a "transmission equipment fault" in Charles County that caused a dip in voltage in the area. The Southern Maryland Electric Cooperative runs the plant where the explosion reportedly occurred.
White House spokesman Josh Earnest said authorities "do not currently see a nexus to terrorism."
Even without evidence of a targeted attack, Admiral William Gortney head of the U.S. Northern Command, acknowledged Tuesday that the United States has "vulnerabilities."
"All of those critical infrastructures are fragile," he said.
The blackout began around 12:45 p.m. local time and spread to dozens of locations around the city, including Voice of America.
At the White House, the power went out briefly before backup generators went into effect, but the complex was soon back to its regular power source.
U.S. Capitol Police told VOA that power had also been restored to the Capitol building.
The outage also hit the Justice Department, the University of Maryland, some of the Smithsonian museums and the Washington metro system.
While some offices stayed open on generator power, other locations were forced to evacuate.