NBC News reported Tuesday that the White House and the U.S. Capitol were put on temporary lockdown following an airspace violation in Washington D.C., according to law enforcement sources.

The Secret Service said in a statement that the brief lockdown was due to a “potential violation of the restricted airspace in the National Capital Region.”

During lockdown also was spotted point of mystery air defense system atop a building across the street from the White House.

Sara Cook, a CBS News producer covering the White House, tweeted out an image showing a missile battery in the roof of a building near the White House.

Andrew Leyden wrote in response to Sara Cook tweet: “There are several types of anti-aircraft missile batteries around DC, near DCA, JBAB, Carderock and other locations. That one you spotted was actually put in place many many years ago.”

According to some sources, the air defense system that was spotted is an element of AN/TWQ-1 Avenger pointed on the roof of the New Executive Office Building (NEOB), a U.S. federal government office building in Washington, D.C.. The building is located at 725 17th Street NW, on the north side of Pennsylvania Avenue. To the south is the Eisenhower Executive Office Building (EEOB), which is next to the White House.

The Drive said that the AN/TWQ-1 is more typically seen mounted on a Humvee, but can be positioned in fixed emplacements, as well. It is armed with the two four-round launchers for the FIM-92 Stinger missile and a .50 caliber M3P machine gun.

Another Twitter user wrote: “Isn´t it quite normal that in/around Washington DC and especially around the hill/White House several defense installations are available? I would be more confused if there are not such things in place?!…as well as they hopefully change positons random to screw up observers!”

As to ‘lockdown’, U.S. Capitol Police confirmed that access to the Capitol Complex buildings was halted “for a short time.” The situation was cleared at 9:12 a.m., Capitol Police said, about 45 minutes after the aircraft was first reported in the restricted airspace.

A spokesperson for NORAD said in a statement later Tuesday that the object could have been “a flock of birds or a weather balloon.”

The event was “resolved without incident,” the spokesperson said.

Spotted during the lockdown: a missile battery in position atop a building across the street from the White House pic.twitter.com/IkmjWby2FI

— Sara Cook (@saraecook) November 26, 2019