China has sentenced a 78-year-old U.S. citizen to life in prison for espionage, a court said Monday, but revealed few details about the previously unreported case.

Such heavy terms are relatively rare for foreign citizens in China, and the jailing of American passport holder John Shing-wan Leung is likely to further strain already-damaged ties between Beijing and Washington.

Leung, who is also a Hong Kong permanent resident, "was found guilty of espionage, sentenced to life imprisonment, deprived of political rights for life," said a statement from the Intermediate People's Court in the eastern Chinese city of Suzhou.

Suzhou authorities "took compulsory measures according to the law" against Leung in April 2021, it said, without specifying when he had been taken into custody.

It was unclear where Leung had been living at the time of his arrest.

A spokesperson for the U.S. embassy in Beijing said they were aware of reports that a American citizen had been recently convicted and sentenced in Suzhou.

"The Department of State has no greater priority than the safety and security of US citizens overseas," the spokesperson said. "Due to privacy considerations, we have no further comment."

The court statement provided no further details on the charges, and closed-door trials are routine in China for sensitive cases.

Foreign ministry spokesman Wang Wenbin declined to comment further on the case at a regular press briefing on Monday.

In Hong Kong, security minister Chris Tang told a news conference Monday the city's authorities were notified of Leung's arrest in 2021.

"The Hong Kong police have carried out follow-up action according to the notification," Tang said, refusing to elaborate further.

The jailing is likely to further damage relations with Washington, which are already severely strained over issues such as trade, human rights and Taiwan.

Washington and Beijing have just ended an unofficial pause in high-level contacts over the United States' shooting down in February of a suspected Chinese surveillance balloon.

U.S. national security adviser Jake Sullivan and top Chinese diplomat Wang Yi held eight hours of talks in Vienna in an apparent breakthrough last week, with both sides describing the meeting as "candid, substantive and constructive".

On Friday, Washington issued a statement condemning the reported sentencing of a Chinese human rights activist for "inciting subversion of state power."

Guo Feixiong, also known as Yang Maodong, was jailed for eight years, according to rights groups. There has been no official confirmation of the sentencing from China.

The U.S. State Department said in its statement its diplomats had been barred from attending the trial in southern China.

"We urge the PRC to live up to its international commitments, give its citizens due process, respect their human rights and fundamental freedoms including freedom of speech, and end the use of arbitrary detentions and exit bans," said U.S. State Department spokesman Matthew Miller.

A Chinese foreign ministry spokesperson said on Monday the country's "judicial authorities act in accordance with the law, and their actions brook no interference".

U.S. President Joe Biden is due to head to Hiroshima for a meeting of leaders of the G7 group of major developed economies.

The G7's relationship with China is expected to be high on the agenda at the May 19-21 summit.

Other high-profile espionage cases in recent years include the arrest in 2019 of Chinese-born Australian writer Yang Jun.

Australia called last week for another of its nationals, jailed journalist Cheng Lei, to be reunited with her family after 1,000 days in detention over "supplying state secrets overseas".

In April, authorities formally charged a prominent Chinese journalist with spying, more than a year after he was detained while having lunch at a Beijing restaurant with a Japanese diplomat, a media rights group said.

Also in April, China approved an amendment to its anti-espionage law, broadening its scope by widening the definition of spying and banning the transfer of any data related to what the authorities define as national security.

The changes to the law will come into force on July 1.

"Chinese authorities have long had an essentially free hand in addressing national security concerns," Chinese law expert Jeremy Daum wrote.

"The laws involved are sometimes amorphous and vague, leading to selective, or even arbitrary, enforcement," he said, adding that the definition of "espionage" was already so broad "it isn't immediately clear what the impact of the expanded definition will be."

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