The US Air Force scrambled jets Tuesday after reports of an unidentified aircraft in restricted airspace over Washington forced a brief lockdown in the White House.

The North American Aerospace Defense Command said in a statement that its jet fighters "are on site and responding."

The plane that allegedly violated the airspace of the US capital city "is not considered hostile at this time," they said.

Washington airspace restrictions were severely tightened after the September 11, 2001 attacks on New York and Washington.