"An Air Force F-16 assigned to Nellis Air Force Base, Nevada, crashed at approximately 10:30 am during routine training on the Nevada Test and Training Range," the Air Force said in a statement.

"The condition of the pilot is not known at this time," it said.

The crash followed two others the day before.

In California, a Marine Corps CH-53E helicopter crashed with four crew aboard.

"The status of all four is presumed dead pending positive identification," the 3rd Marine Aircraft Wing said.

And in Djibouti, a Marine AV-8B Harrier jet crashed after the pilot ejected during takeoff.

"Doctors said the pilot was in stable condition," US Naval Forces Central Command said.

US Defense Department chief James Mattis secured a record budget last month for the Pentagon, which will allow investments that have been on hold for several years, including in the Navy, which is overstretched in foreign theaters, and the Air Force, which suffers rapid pilot turnover due to more lucrative private sector options.