Two US Air Force F-22 Raptor stealth jet fighters fly near Andersen Air Force Base in this handout photo dated August 4, 2010. [Photo/Agencies]

WASHINGTON - The US Air Force has stopped flying Lockheed Martin's F-22 Raptor fighter jets indefinitely due to concerns about faults in the system that supplies oxygen to pilots, the military said on Thursday.

The Air Force said it issued an order on Tuesday to stop flying the jets "until further notice" after reports of "oxygen system malfunctions."

"The stand-down provides Air Force officials the opportunity to investigate the reports and ensure crews are able to safely accomplish their missions," the Air Force said in a statement.

The Raptor is the premier US fighter, with cutting-edge "fifth-generation" features, including shapes, materials and propulsion systems designed to make it appear as small as a swallow on enemy radar screens.