A military jet crashed during exercises Wednesday over a vast U.S. Air Force reserve in central Nevada, officials said.

The F-16 fighter from Nellis Air Force Base crashed on the Nevada Test and Training Range, said base spokesman Staff Sgt. Jason Coulliard.

The condition of the pilot or pilots and the location on the 4,500-square-mile (11,655-square-kilometer) training range were not immediately made public.

A statement said emergency crews were at the scene and an accident investigation had begun.

The incident was the third U.S. military aircraft crash this week.

Four crew members were killed when a Marine CH-53E Super Stallion helicopter crashed Tuesday in California during a training mission along the U.S.-Mexico border west of El Centro.

The same day, a Marine Harrier jet crashed during takeoff from an airport in the East African nation of Djibouti. The pilot ejected and was medically evaluated.

Last September at Nellis, a U.S. Air Force pilot died of injuries after a crash on the training range about 100 miles (160 kilometers) northwest of the base.

Officials did not disclose the type of aircraft Lt. Col. Eric Schultz had been piloting. He was assigned to a military command that conducts research and weapon system tests.

In January, an unspecified military aircraft aborted takeoff and caught fire at Nellis, but no serious injuries were reported.

(AP)