Wenheng Zhao, 26, pleaded guilty in October to passing on information to Chinese intelligence for bribes.

Mr Zhao was a petty officer working at a California naval base.

He passed on information about military exercises, operational orders and critical infrastructure From 2021 to 2023, US officials said.

Specifically, he provided information about the US Navy's large-scale drills in the Indo-Pacific region, as well as electrical diagrams and blueprints for a radar system located at the US base on the Japanese island of Okinawa.

The US Navy's base there in Okinawa is critical to its operations in Asia. The US has made what it calls the "Indo-Pacific" region a key security priority, and in recent years has worked on shoring up alliances there to counter China's ramped-up military presence.

In the past few years it has expanded the naval drills it operates with allies in the region. However, US authorities gave no indication that information about other countries' naval drills was compromised.

Zhao, who had security clearance and worked at Naval Base Ventura County in Port Hueneme, had specifically entered restricted military and naval installations "to collect and record" information, the US Justice Department said.

He also used "sophisticated encrypted communication methods" to pass on the information, destroyed evidence and concealed his relationship with a Chinese spy.

He was paid at least 14 separate bribes between August 2021- May 2023, to a total of at least $14,866 (£11,650).

Zhao is a naturalised US citizen who was born in China. He immigrated to the US in 2009, became a citizen in 2012 and enlisted in the navy five years later.

He was arrested last August in California and pleaded guilty to the spying charges in October.

On Monday a Californian district court sentenced him to 27 months in jail. He had faced a maximum 20 year sentence.

There were no reports of any of his comments. Authorities have also not provided information as to the motivation for his betrayal, beyond financial reasons.

In October, following Zhao's guilty plea, US Justice Department Assistant Attorney General Matthew Olsen said China's intelligence services "actively target clearance holders across the military, seeking to entice them with money to provide sensitive government information."

On Monday he reiterated the warning.

"Mr Zhao betrayed his solemn oath to defend his country and endangered those who serve in the US military," he said.

Mr Olsen added that US authorities were committed to combatting Chinese government efforts to "undermine our nation's security".

Another US Navy member was also arrested last year, around the same time as Zhao, and charged with spying offences. Jinchao Wei, 22, a naturalised US citizen, is accused of conspiring to send national defence information to a Chinese agent.

Wei had served on the amphibious assault ship the USS Essex and was accused of handing over dozens of documents, photos and videos detailing the operation of ships and their systems to China.

It is unclear if the same Chinese agent is alleged to have contacted both men.

China's embassy in Washington on Monday said it was not aware of the details of Zhao's case. It accused the US government and media of hyping up espionage cases, many of which it said were based on unfounded allegations.

By Frances Mao