On Monday morning during rehearsals for the Inauguration Day ceremonies, a fire near the US Capitol building triggered a rapid lockdown as lawmakers and staffers were advised to stay away from windows and “seek cover” if outside.

The Capitol complex was briefly locked down due to an “external security threat,” U.S. Capitol Police said, after a fire was reported several blocks away under a nearby bridge.

After the lockdown was declared via intercom, staff attending a rehearsal for the inaugural ceremonies were evacuated from the area and rushed into the US Capitol visitor centre. The fire was not thought to be a threat to the inaugural rehearsal, officials later said.

Reports of smoke rising from behind the building appeared to come from a nearby fire in the 100 block of H St SE.

A law enforcement official told NBC News that what turned out to be a fire at a homeless encampment prompted the security alert.

The DC fire department said in a statement there were no injuries in the incident, adding: “This accounts for smoke that many have seen.”

U.S. Secret Service announced that a small fire has been extinguished.

“Public safety and law enforcement responded to a small fire in the area of 1st and F streets SE, Washington, D.C. that has been extinguished. Out of an abundance of caution the U.S. Capitol complex was temporarily shutdown. There is no threat to the public.”

Updated: “The lockdown at the U.S. Capitol has been lifted. The fire under the bridge on I-295 at First and F Streets, SE, has been contained by DC Fire. The investigation into the incident is continuing.”

The Capitol is currently operating as a military zone ahead of Biden’s inauguration this week. There are currently 7-foot barriers that have been staged around the Capitol, its office buildings, and the Supreme Court. The National Mall is temporarily closed to public access in the days leading up to and following the inauguration on Jan. 20.

Roughly 25,000 National Guard troops are deployed to D.C. in order to boost security around the inauguration.

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