NORAD has confirmed that no plane was found.
Original report: The White House and the U.S. Capitol were in lockdown after an airspace violation in Washington, D.C., multiple news outlets reported.
The lockdown began just before 9 a.m. but was lifted about 20 minutes later, NBC News reported.
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U.S. Northern Command confirmed that military aircraft responded.
But it was not believed to be a hostile aircraft at the time.
The plane caused a "national event conference," or a meeting of senior national security officials from a variety of agencies, to monitor the situation, CNN reported.
The incident also caused everyone to leave the North Lawn of the White House, NBC News reported. Reporters were not permitted to leave the briefing room while under lockdown.
The White House is currently under lockdown - reporters have been evacuated from the North Lawn and are not able to leave the briefing room.