Updated at 2:30 p.m. ET

Large portions of Washington, D.C., were hit by power outages Tuesday, momentarily plunging the White House and other buildings into darkness.

The Pepco utility company says the culprit was a transmission line in southern Maryland that caused "a dip in voltage" shortly before 1 p.m. ET. The power company says there was never a loss of permanent supply of electricity, but the situation caused some customers to move to their backup systems, which is what caused the dip in voltage.

Pepco says there are no current supply problems.

The outages affected commercial, residential and federal buildings across the nation's capital. The Smithsonian said it had evacuated several of its museums because of the outages. Many, but not all, switched to backup power.

Power at the State Department was out for more than 90 minutes. NPR's Michele Kelemen says reporters were being briefed on the situations in Yemen and Cuba, when the power went out. State Department spokesperson, Marie Harf, decided to continue with the daily briefing despite the darkness.

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