Jia Jia disappeared Tuesday shortly after going through customs at Beijing international airport while preparing to board a flight to Hong Kong where he was to attend an academic conference, according to a close friend cited by Amnesty International.
"Because of his implication in a case, Jia Jia was detained at Beijing airport terminal on March 15," said lawyer Yan Xin on his WeChat account, adding that the information came from the city's Public Security Bureau.
Amnesty and the Committee to Protect Journalists linked the journalist's disappearance to the publication this month on the Chinese news website Wujie News of an open letter calling for the resignation of Chinese President Xi Jinping.
The letter, which was rapidly removed, was signed "Loyal Communist Party members", but little else is known about its authorship.
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"His going missing is most likely related to the publishing of the letter and perhaps the authorities' implication of his involvement or knowledge of the letter," Amnesty China researcher William Nee told AFP earlier.
Since Xi came to power the Chinese Communist Party has increased pressure on civil society, arresting or questioning more than 200 lawyers and human rights activists.
China is currently in the spotlight over the disappearance last year of five Hong Kong booksellers who reappeared on the mainland, as well as the use of televised confessions from suspects.
The five booksellers were from Hong Kong's Mighty Current publishing house, known for its salacious titles critical of Beijing.