"The aircraft had completed its mission and was returning to base when the crash occurred," Air Force Capt. David Small, a spokesman for the US Central Command Air Forces, or CENTAF, said by telephone from the Gulf region.

Small refused to say where the U-2, which was based with the 380th US Air Expeditionary Wing in the United Arab Emirates, had crashed but added that the incident was under investigation. The jet went down at 7:30 p.m. EST Tuesday, which was Wednesday in the Asia region.

Small said U-2s had been flying daily over Iraq and Afghanistan in support of US and allied forces fighting in the two countries.

The United Arab Emirates news agency WAM said the aircraft crashed while trying to land at one of its military bases, and that the UAE was helping in the investigation being conducted by the US military.

The agency said the US had an agreement with the UAE that allowed it to use some of its military facilities.

The single-seat, high-altitude reconnaissance and surveillance plane, a veteran of the Cold War with the former Soviet Union, is unarmed but flies at altitudes that make it impervious to many ground-fired weapons.

CENTAF is the air arm of the US Central Command, which is responsible for US military operations in the Gulf, Middle East and parts of Asia.