Washington DC - Secretary of State Marco Rubio announced on Thursday that the State Department has designated a US citizen held by China on espionage charges as "wrongfully detained" and demanded his release.

Min Zin, a political analyst at a policy think tank focusing on neighboring Myanmar, was taken into custody in the southwestern Chinese province of Yunnan on June 3, the US government said.

"Secretary Rubio has formally designated US citizen Min Zin as wrongfully detained," Assistant Secretary Dylan Johnson said in a statement to X. "We call on Beijing to release all US citizens arbitrarily detained or exit banned in China."

"There are now two wrongfully detained US citizens in China: Mr Zin and Dr Youlin Chen," Johnson said in a separate statement. "The safety and security of U.S. citizens is the State Department’s top priority."

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"We will continue to advocate for Mr Zin and call for the release of all US citizens who are arbitrarily detained or exit banned in China."

Johnson said Min Zin "had traveled to attend an academic conference at the invitation of the Chinese government" when he was detained.

The Chinese foreign ministry has said he was held "on suspicion of engaging in espionage activities that endanger China's national security."

Min Zin is a founder of the Institute for Strategy and Policy Myanmar (ISP-M), which researches the political, resource, and conflict dynamics of Myanmar, a country plunged into civil war by a 2021 military coup.

Some ISP-M publications detail China's influence in the borderlands of Myanmar, where Beijing is accused of supporting both rebel factions and the military in pursuit of its interests.

Rubio's decision to move forward with the designation comes only a month before Chinese President Xi Jinping is due to visit with President Donald Trump in Washington.