From Mike Mount
CNN Washington Bureau

WASHINGTON (CNN) -- Two Air Force F-16s were scrambled early Fridaymorning to investigate a low-flying, unknown aircraft close to the restrictedflight zone over Washington, according to an official at the North AmericanAerospace Defense Command.

A Pentagon official said that an aircraft appeared on radar in the 15-milerestricted flight zone around Washington.

"The pair of jets were scrambled from Andrews Air Force Base in Marylandat about 1 a.m. Friday to investigate reports of an aircraft in the Washington,D.C. Temporary Flight Restriction Area," said Maj. Barry Venable, a spokesmanfor NORAD.

Venable would not say how long the F-16s were in the air.