An American seismologist with ties to U.S. government research has been held in China for nearly two years on espionage allegations, according to his family and advocacy groups. Dr. Youlin Chen, who was born in Beijing and is now a U.S. citizen, was detained by Chinese state security officers at a Beijing airport in November 2024 as he prepared to return to his home in Boston.

Chen’s family made the case public this week, seeking to increase international pressure on China to release him amid ongoing tensions between Washington and Beijing. The Chinese authorities have accused Chen of spying, likely linked to his work analyzing seismic data to monitor nuclear tests, but his family and supporters contend the charge is baseless.

U.S. officials have raised Chen’s detention directly with Chinese counterparts, calling for his immediate release, the State Department said Tuesday. However, analysts caution that Beijing is unlikely to quickly reverse course, reflecting broader challenges in the Sino-American relationship. Chen’s detention comes amid heightened Chinese surveillance under President Xi Jinping and increased scrutiny of individuals, particularly Chinese-born scientists and scholars, engaged in research considered sensitive by the Chinese government.

Chen’s work included contract research for the U.S. government and military agencies aimed at detecting and interpreting seismic signals from North Korea’s nuclear tests, leveraging data from stations in China. While there is no indication that Chen investigated potential Chinese nuclear tests, suspicions over such activity have grown in Washington, in part due to unconfirmed reports of a small Chinese nuclear test in 2020.

Global Reach, an organization supporting Americans detained overseas, stated that Chen’s research was transparent and collaborative, with no classified elements. His employer, EMR Solutions and Technology, confirmed his work involved publicly accessible data and that the company provides security briefings for employees traveling abroad.

Chen traveled to China in 2024 to visit family and celebrate his mother’s 80th birthday. He also delivered lectures at two universities during his visit. Following a lecture at China University of Geosciences in Beijing, Chen was stopped at the airport, after which contact with him ceased. Chinese officials confiscated his electronic devices and reportedly accessed his emails and online accounts.

Senator Ed Markey of Massachusetts, citing information from Chen’s wife, Rufang Rong, has advocated for Chen’s release. According to Senator Markey, Chen’s phone location data indicates it was at a Beijing state security bureau office following his detention. Chen has been formally arrested since May 1 but has not yet been brought to trial.

American consular officials have been allowed monitored visits with Chen. His wife reported that his health has deteriorated during detention, including significant weight loss and lack of access to medications for chronic conditions such as diabetes and hypertension.

In March, Senator Marco Rubio designated Chen as “wrongfully detained,” a move signaling U.S. recognition that his imprisonment is politically motivated. Advocacy groups say the designation heightens pressure on China and underscores Chen’s innocence.

China’s foreign ministry has neither confirmed nor denied Chen’s detention but stated that the country follows the rule of law and denies wrongful detentions. Similar cases involving Chinese-born American citizens detained on espionage accusations have complicated U.S.-China relations for years. In a notable precedent, China released Xue Feng, an American geologist born in China, in 2015 after seven years of detention on similar charges, following extensive diplomatic engagement.

As diplomatic efforts continue ahead of planned summits between U.S. President Joe Biden and President Xi Jinping, Chen’s case remains an unresolved point of tension between the two nations.