The U.S. and Qatari governments are investigating the inadvertent launch of a missile from a U.S. military base in the gulf Arab state.

A Pentagon spokesman, Lieutenant General Carter Ham, says the Patriot missile self-destructed in the air, as it was supposed to do. The debris landed on farmland near the base, and caused no casualties. The spokesman says authorities have secured the debris area.

He told a Pentagon news conference Tuesday that a U.S. military unit was conducting a training exercise when the missile was launched. He said it is unclear how or why the missile was launched.

The Patriot missile is a defensive weapon, designed to intercept and destroy incoming missiles and aircraft.

Qatar hosts the U.S. Army's Central Command, which oversees U.S. forces in the Middle East.

Some information for this report was provided by AFP and AP.