A Chinese-born US seismologist known for US-supported studies on identifying North Korean nuclear tests has been held in China for almost two years and now faces espionage accusations, according to his spouse, American legislators and two groups focused on hostage issues.

The situation involving Youlin Chen, disclosed publicly here for the initial time, introduces added friction into the strained ties between the two nuclear powers and arrives as President Donald Trump aims to maintain steady relations after the previous trade conflict.

US Secretary of State Marco Rubio designated Chen, aged 54, as wrongfully detained on March 19, elevating his release to a key priority. The Trump team has avoided a public statement to preserve room for senior diplomatic efforts to secure his freedom, according to his wife Yufang Rong.

A US official aware of the matter indicated the administration remains focused on achieving his release from unjust detention. The official requested anonymity due to the sensitive nature of ongoing talks.

Chen, who gained US citizenship in 2011 and resides in Boston, stands as the sole American currently held in China and labeled wrongfully detained, per his wife and advocacy groups.

Rong noted that White House and State Department officials informed her Trump raised the detention during a May state visit to Beijing with Chinese leader Xi Jinping, who agreed to review the matter. Xi's administration has taken no further steps, she stated.

The US official stopped short of confirming direct discussion between Trump and Xi on Chen but noted their strong personal rapport. This represents one element among many in bilateral ties, with no single matter dominating.

In a Reuters discussion, Rong voiced worry that Beijing may have predetermined Chen's guilt on espionage charges ahead of any trial, an offense that can bring life imprisonment or even capital punishment in severe instances under Chinese law.

I believe they will convict him regardless and conduct the proceedings in private, said Rong, herself a seismologist who does not work with her husband on his projects.

At least a dozen Americans held unjustly in China

The Foley Foundation, which tracks Chen's situation, estimates he is one of at least 12 Americans held unjustly in China, including those under exit restrictions, according to director Elizabeth Richards.

President Trump has stated clearly his desire for every American detained overseas to return home, and he has facilitated the reunion of over 100 individuals with their families since assuming office this term, said deputy White House press secretary Anna Kelly.

The Office of the US Special Presidential Envoy for Hostage Affairs and the Chinese embassy offered no immediate comment on requests.

US embassy staff have met with Chen multiple times, yet Chinese authorities remain present, limiting his ability to speak openly, Rong explained. She hired a Chinese attorney who gained access only after more than 13 months of detention.

Chinese officials have questioned her husband over 100 times regarding his research on seismic signals from North Korean nuclear tests, Rong added.

Eric Lebson, a former national security official whose group Global Reach advises the family, believes China seeks to leverage Chen's knowledge to enhance its capacity to hide underground nuclear tests via a method known as decoupling.

Lebson noted similar views from nuclear testing specialists consulted by the organization.

US charges China with concealing nuclear tests

The Trump administration accused China in February of attempting to obscure a low-yield underground nuclear test on June 22, 2020, through the decoupling technique that involves detonating a device in a large subterranean chamber to lessen shock wave strength.

China, which like the US has signed but not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty, rejects claims of conducting the test.

Lebson stated Chen works for a US government contractor and has never held security clearance or engaged in classified activities.

His studies on seismic waves from North Korean blasts received funding from the State Department and Air Force Research Laboratory, Lebson said, noting collaboration with Chinese academics using publicly available data accessible online.

A December 2020 paper by Chen, examined by Reuters, analyzed the scale of North Korea's six known nuclear tests and methods to differentiate their seismic patterns from earthquakes.

The cover page indicates the work was prepared for the State Department's arms control bureau and approved for public release.

Human rights organizations have noted that China's state secrets law grants authorities wide latitude to retroactively classify public data as national security matters, potentially affecting anyone who handled or shared previously open information.

Chen was detained by state security at Beijing International Airport on November 5, 2024, while preparing to return to Boston after family visits and lectures at two universities, according to Rong and Lebson.

Chinese-American detainee faces difficult conditions, wife reports

Early in his detention, Rong said Chen endured harsh treatment, including prolonged sitting on a hard stool without permission to stand, read or exercise, plus denial of diabetes medications and other health needs.

Since then, details on his confinement have been hard to obtain, though she reported he has lost 30 to 40 pounds, receives inadequate meals low in protein, fruits and vegetables, and gets only low-grade medications.

He was charged with espionage on May 1, 2025, but has not yet faced trial. The case may arise again during Xi's planned September visit to Washington, as mentioned by Trump.

US Senator Ed Markey, a Massachusetts Democrat who joined two colleagues in a December 17, 2025, letter pressing Rubio to designate Chen as wrongfully detained, expressed deep concern for his safety and well-being.

It is my hope that greater focus on his unjust detention will compel the Chinese government to release Dr. Chen, Markey said in a statement.