China has arrested a US nuclear expert on espionage charges, his family said.

China has detained an American seismologist monitoring nuclear tests for two years on espionage charges, his family said.

Chen Yulin, 54, was arrested in November 2024 while on a trip to Beijing to visit his family, according to the hostage advocacy group Global Reach. The family decided to speak out after seeing no sign that Beijing would release Chen.

His wife, Rong Yufang, also a seismologist, said Chen worked closely with Chinese colleagues, adding that the charges were “wrong and inconsistent with the cooperative nature of the people and his work.”

His published work focuses on North Korea, a close ally of China and long under sanctions for its nuclear weapons program and underground testing.

It is unclear how Chen’s work has affected Beijing’s nuclear program. US intelligence agencies say China is developing new weapons and conducting secret tests, which Beijing denies.

Asked about the case, China’s foreign ministry said in a press release on Tuesday that “judicial authorities will handle cases in accordance with the law.”

“There is no such thing as wrongful arrest,” said Lin Jian, a spokesman for the ministry. Espionage in China can be punishable by life imprisonment or death.

Chen is the only American citizen currently classified as “wrongfully imprisoned.”

“I have not been able to speak to my husband for over 600 days and I am concerned for his health and safety,” Rong said in a statement through Global Reach.

In an interview with Reuters, she said Chinese authorities questioned her husband more than 100 times about his work and that he was not allowed to see a lawyer during the first 13 months of his detention.

Born in China, Chen He became a US citizen in 2011. He lives in Boston, Massachusetts.

He specializes in using seismological data to detect nuclear tests and has done several projects funded by the US government. Rong said that the work he does with his colleagues in China is always done “transparently.”

He added, “The Chinese government is doing exactly the kind of people-to-people relations that it wants.”

Chen’s work included a study of seismic data recorded across Asia, including China, to improve methods for nuclear-test control and production estimation in December 2020.

According to Global Reach, there are “suspicions within the US government that Chen’s arrest was in violation of China’s Comprehensive Nuclear-Test-Ban Treaty.”

According to the group, Chen’s expertise will give China the opportunity to learn as much as possible about US earthquake detection methods and develop countermeasures that will allow them to break the deal.

The treaty seeks to ban all nuclear tests on Earth, but several “nuclear-capable” states have yet to ratify it. Among them are the United States and China, which have established a voluntary ban on explosive nuclear testing.

In June 2020, during Donald Trump’s first term as president, the administration accused Beijing of conducting a secret underground nuclear test at the Lop Nur facility in the northwest. China has dismissed the claims as baseless and politically motivated.

Another US-based hostage advocacy group, the Foley Foundation, expressed concern about Chen’s health, saying he suffers from diabetes, high blood pressure and high cholesterol.

He needs reliable access to treatment and care that is not available while he is being held arbitrarily, the group said.

U.S. Sen. Edward Markey, Democrat of Massachusetts, said Beijing’s “treatment of Chen could weaken the partnership (with the U.S.) and prevent other academics from connecting with their colleagues in China.”

“It is my hope that the spotlight on his unjust imprisonment will force the Chinese government to do the right thing and release Chen,” he wrote in a statement on Tuesday.

The details of Chen’s arrest came a month after China confirmed his arrest. Another American scholar, Min Zinn.Director of a think tank focusing on Myanmar.

Beijing accuses Min Xi of spying and endangering China’s national security.