Pepco, the D.C. electric services provider, initially said it had scattered reports of outages for "unknown" reasons, and that it was looking into the matter. Government officials later pointed to an explosion at a southern Maryland power facility as the likely cause for the regional issue.
Department of Homeland Security officials said just after the outage began that they were looking into the outage, but believed at the time there was no reason to believe the power failure had any connection to terrorism or other criminal activity.
The utility company said in a 1:35 p.m. ET update that it recorded 129 active outages and 2,179 affected customers (which include buildings and office spaces). Pepco told CNBC that a brief dip in D.C. area voltage caused some customer's systems to automatically switch to a backup system—there was never any full loss of electricity and customers could resume use of street power whenever they wanted, it said.
Washington D.C. area outages on Tuesday afternoon, according to Pepco.
A U.S. official said the White House was without power for a few minutes. The daily press briefing there was delayed because of the outage. By 2:15 p.m. ET, the White House had gone back to its normal power source, White House Press Secretary Josh Earnest said.
He added that President Barack Obama did not appear to have noticed the switch from normal power to backup during the brief outage.
The State Department's daily news briefing, meanwhile, was suspended after power was lost. A department announcement said the main building and other nearby buildings were affected because electricity feeders were down.
The U.S. Capitol complex was operating using a backup generator, one congressional aide said. A Capitol police spokeswoman said at about 1:45 p.m. ET that all power had been restored to the grounds there, but cautioned that the facilities could experience additional outages or surges.
The University of Maryland at College Park said it suffered a campus-wide power outage, and that it would close for the rest of the day. Other reports about outages in Maryland's Prince George's and St. Mary's counties came in across social media.
Some metro stations in Washington were running on emergency lighting, according to the city's transportation authority. Several area museums were affected by the outage. The National Portrait Gallery, the Air and Space Museum and others were evacuated, the Smithsonian Institution said in a tweet.
The State Department suffered a similar outage on December 15, which Pepco blamed on construction at the time.
—NBC News and Reuters contributed to this report.