Outages stretched from downtown Washington into neighboring Maryland, knocking power out for more than 2,500 people, according to area power companies.

Most outages were brief, but computer systems were downtown offices and access to Metro trains were disrupted.     

Washington power provider Pepco said the outage was caused by a dip in voltage as a result of an issue with the transmission line.

"There was never a loss of permanent supply of electricity to customers," Pepco said.

Electricity was restored to normal by mid-afternoon and the company had dispatched teams to look into how it happened.

Outages were reported at more than 2,100 premises and households in Washington, according to Pepco, and more in Maryland suburbs southeast of the capital. Major government buildings were not spared, including the White House, which lost power briefly.

Back-up generators kicked in promptly to restore lights and computers that were knocked out for several seconds, said a reporter.
    
White House spokesman Josh Earnest said there was no indication that the outage was a result of a security breach.

"I do not currently see a nexus to terrorism," he told reporters.

The State Department went dark in the middle of a pressbriefing, which continued on for a time in the dark, a spokeswoman reading from her notes with the light from her cellphone.

Lights had returned to the building by mid-afternoon. Power at Capitol Hill flickered on and off intermittently but was later restored, an official there said.

The Department of Homeland Security ruled out foul play, and said it was "closely monitoring the reports of power outages affecting parts of Washington, DC."

"At this time, there is no indication that this outage is the result of any malicious activity," DHS added.

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