The White House was briefly placed on lockdown Tuesday morning after an aircraft entered restricted airspace in the Washington area.
The event caused senior national security officials across the agencies to convene to coordinate and monitor the situation, according to a US defense official, and aircraft were deployed to monitor the situation, US Northern Command tweeted.
"Senior officials across the interagency are monitoring the situation on a national event conference call. NORAD aircraft are on site and responding," Lt. Col. Chris Mitchell, a Pentagon spokesman, told CNN.
The White House lockdown has been lifted.
Two US Capitol Police sources said the situation is being classified as an "aircon," which is an as-yet unidentified incoming aircraft.
The US Capitol Police have also given an all-clear to the Capitol Hill complex, according to two US Capitol Police sources.