China’s Foreign Ministry spokesman Lin Jian told a daily press briefing that Min Zin, a U.S. citizen, has been placed under criminal detention “on suspicion of conducting espionage and endangering China’s national security” and that he is being investigated under “criminal coercive measures.” Lin said the U.S. Consulate General in Guangzhou had been informed and that Min Zin’s legal rights would be respected.

The detention, previously reported by the New York Times, adds another point of friction between the world’s two largest economies weeks after Trump and Xi met in Beijing. In addition to trade and military disputes, senior U.S. officials have pressed Beijing to release Ezra Jin and Jimmy Lai. Trump said he raised both men’s cases with Xi during their summit last month.

Min Zin was a student activist and journalist in Myanmar, also known as Burma. He went into hiding in 1989 and fled the country in 1997 as the ruling junta tightened its grip, according to articles published by the University of California, Berkeley, on its website. He earned a master’s degree in journalism at Berkeley and later became a teaching fellow there, also pursuing a doctorate in political science.

In 2008, Min Zin’s brother — also a journalist — was sentenced to seven years in prison by Myanmar’s ruling junta, Min Zin wrote in a Wall Street Journal opinion piece that year.

Min Zin helped found the Institute for Strategy and Policy Myanmar, an independent think tank, in 2016. The group, based in Chiang Mai, Thailand, said its goal is “to promote democracy, a federal union, and strengthen civil society in Myanmar.” In an annual report published in January, ISP-Myanmar wrote that “Myanmar appears to be sleepwalking into China’s sphere of influence.” Myanmar President Min Aung Hlaing is scheduled to pay a state visit to China next week.

ISP-Myanmar did not immediately respond to a request for comment. Spokespeople for the State Department also did not respond.

China’s Foreign Ministry did not provide the location or date of Min Zin’s arrest. He had been invited to the country by a Chinese university, according to a person familiar with the situation, who did not offer further details.

Dozens of American citizens remain barred from leaving China, often because of connections to continuing legal disputes. The U.S. Embassy in Beijing has sought, with varying degrees of success, to free these Americans from their effective confinement within China’s borders.