The US State Department said on Thursday that it had determined after a detailed investigation that Min Zin , an American political analyst of Chinese descent detained by Beijing last month, was being improperly held.

That formal designation shifts the case from a State Department consular issue to one handled by its presidential office dealing with hostage affairs.

Thursday’s terse statement, which said the decision was made by Secretary of State Marco Rubio, adds another irritant to the fraught bilateral relationship just weeks before Chinese President Xi Jinping and US President Donald Trump