Gerald Brown, 65, was arrested in Indiana after having recently returned to the United States from China, where he had been since December 2023, a Justice Department statement said.

He is accused of having "conspired with foreign nationals to provide combat aircraft training to pilots in the Chinese Air Force" without a required license from the US State Department, the statement said.

FBI director Kash Patel posted on X: "Major story... the FBI and our partners have arrested a former US Air Force Pilot who was allegedly training pilots in the Chinese military."

Brown had a 24-year career in the US Air Force during which he "commanded sensitive units with responsibility for nuclear weapons delivery systems, led combat missions, and served as a fighter pilot instructor and simulator instructor on a variety of fighter and attack aircraft."

He had retired from the military in 1996 and worked as a cargo pilot, the statement said, but he later began a role as a US defense contractor training pilots to fly the A-10 and state-of-the-art F-35 fighter jets.

He allegedly began negotiating a contract in August 2023 with Stephen Su Bin -- a Chinese national who was imprisoned in the United States for four years beginning in 2016 over another espionage scheme -- and traveled in December 2023 to China to begin his training job.

"The Chinese government continues to exploit the expertise of current and former members of the US armed forces to modernize China's military capabilities," said Roman Rozhavsky, an official with the FBI's Counterintelligence and Espionage Division.

"This arrest serves as a warning that the FBI and our partners will stop at nothing to hold accountable anyone who collaborates with our adversaries to harm our service members and jeopardize our national security," he added.