Chinese authorities have detained an American scholar known for his research on Myanmar and Chinese foreign policy on suspicion of espionage, China's Foreign Ministry said on Friday.

Foreign Ministry spokesperson Lin Jian said the scholar, Min Zin, is suspected of “engaging in espionage activities that endanger China’s national security.”

The arrest is unusual, as China rarely detains US citizens on national security-related accusations. The development comes about a month after US President Donald Trump met Chinese President Xi Jinping in Beijing as both countries sought to improve strained bilateral ties.

According to a Myanmar activist familiar with the matter, Min Zin went missing on June 3 after travelling to Kunming in China’s Yunnan Province to attend a conference. The activist, who requested anonymity due to concerns about possible repercussions, said Min Zin had visited China several times in the past.

Min Zin was involved in Myanmar’s 1988 pro-democracy student movement, which was violently suppressed by the then military-backed government. He later received asylum in the United States. The activist said Min Zin is not currently involved in direct political activism.

He is the founder of ISP Myanmar, a think tank that has published research on Chinese foreign policy and economic engagement with Myanmar, including studies on Myanmar’s rare earth exports to China. The organisation has also maintained regular exchanges with Chinese research institutions.

Min Zin is currently pursuing a PhD at University of California, Berkeley.