China has arrested a US scholar who writes about Myanmar and Chinese foreign policy on suspicion of spying.

Min Zin was suspected of “engaging in espionage activities that endanger China’s national security,” China’s ministry of foreign affairs spokesperson, Lin Jian, said on Friday.

It is uncommon for Beijing to arrest a US citizen on national security allegations, and the case comes just a month after Donald Trump met the Chinese president, Xi Jinping, in Beijing as the two countries aim to reset their tumultuous relationship.

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

Min Zin was a student activist in Myanmar’s 1988 uprising, a student-led movement the then-government reacted to with military force; he later sought asylum in the US. He was not currently involved in any direct activism work, the activist said.

Min Zin founded a thinktank called ISP Myanmar, which in recent years has been writing about Chinese foreign policy and trade with Myanmar, located on China’s south-west border. The thinktank exchanged ideas with Chinese thinktanks, and had published reports on issues such as Myanmar’s rare-earth exports to China.

He is also a PhD candidate at the University of California, Berkeley.