Washington, Nov 26 (AFP) The US Air Force scrambled jets Tuesday after reports of an unidentified aircraft in restricted airspace over Washington forced a brief lockdown of the White House and Capitol.

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.

"The White House was locked down this morning due to a potential violation of the restricted airspace in the National Capital Region," the US Secret Service, which protects President Donald Trump, said in a statement.

"The lockdown has been lifted at this time," they said.

The alert lasted less than an hour. The Capitol Police said the report of a possible aircraft in restricted airspace came in at 8:27 AM (1327 GMT) and the situation was cleared at 9:12 AM "without incident".

There was no information about what Trump and his wife Melania did during the alert.

The alert evoked memories of the September 11, 2001 attacks when Al Qaeda jihadists piloted a passenger jet into the Pentagon and were believed to be targeting another at the White House or Congress before it crashed in a field in Pennsylvania.

Two other jets were flown by the attackers into the World Trade Center in New York.

Washington airspace restrictions were severely tightened after those attacks, which left nearly 3,000 dead.

And surface to air missile batteries have been installed around the city to target potentially attacking aircraft.

In history a number of Americans have flown aircraft into downtown Washington in protest.

In 1974 Robert Preston, a despondent army private who was 20 years old landed a military helicopter on the White House lawn, after police cars tracked him on the ground and Secret Service agents fired at him with shotguns.

In April 2015 Florida mailman Doug Hughes, angry about how big money was allegedly corrupting US politics, flew undetected in a small gyrocopter into downtown Washington, landing it just outside the Capitol building.

He landed without incident, was arrested and a year later was sentenced to 120 days in jail for the felony crime of operating the aircraft without a pilot license. (AFP)

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