A small plane unintentionally intruded the restricted airspace over Washington, D.C., Wednesday, putting the Capitol building on alert but posing no imminent threat.

The US Capitol building is seen in Washington in this January 28, 2008 file photo. A small plane unintentionally intruded the restricted airspace over Washington, D.C., Wednesday, putting the Capitol building on alert but posing no imminent threat. [Agencies]

A short time later, Capitol Hill police gave the all-clear and said the aircraft landed outside the restricted zone, according to wire and TV reports.

There was no evacuation in the Capitol building and "things are back to normal," police said.

The North American Aerospace Defense Command (NORAD) said the plane, a small Cessna, has landed at a regional airport in Leesburg, Virginia, after the intrusion.