MYANMAR: An American scholar who writes about Myanmar and Chinese foreign policy was arrested by authorities in China on suspicion of spying, China’s foreign ministry said Friday.

The scholar, Min Zin, was suspected of “engaging in espionage activities that endanger China’s national security,” said China’s Ministry of Foreign Affairs spokesman Lin Jian.

It is uncommon for Beijing to arrest a U.S. citizen on national security allegations. The case comes just a month after U.S. President Donald Trump met with Chinese President Xi Jinping in Beijing as the two countries aim to reset a tumultuous relationship.

A Burmese activist who knows Min Zin said he disappeared June 3 after going to Kunming, in China’s Yunnan province, for a conference. The activist, who spoke on condition of anonymity out of fear of government retribution and arrest, said Min Zin had visited China multiple times before.

Min Zin was a student activist in Myanmar’s 1988 uprising, a student-led movement that the government at the time reacted to with military force. He eventually sought asylum in the U.S. He was not engaged in any direct activism work currently, said the activist.

Min Zin is the founder of a think tank called ISP Myanmar, which in recent years has written about Chinese foreign policy and trade with Myanmar, located on China’s southwest border. The think tank was involved in regular exchanges with Chinese think tanks, and had published on issues such as Myanmar’s rare earth exports to China.

Min Zin is also a Ph.D candidate at the University of California, Berkeley.

Amnesty International, the human rights organization, called for Min Zin’s immediate release.

“The circumstances around Min Zin’s mysterious arrest are extremely concerning, as is the apparent charge of espionage,” said Joe Freeman, a Myanmar researcher for the group.