A lawyer for prominent Chinese columnist Jia Jia, who went missing last week, has confirmed he has been detained by Beijing police.
Yan Xin said police had told him that Mr Jia was taken away at the airport last week, before boarding a flight to Hong Kong.
Mr Jia is said to be linked to a letter calling for the resignation of Chinese President Xi Jinping, published on a state-linked site earlier this month.
The letter was quickly taken down.
Mr Yan posted on his WeChat account that police said Mr Jia was “suspected to be involved in a certain case” but did not give any details.
Activist groups and Hong Kong media have said Mr Jia warned the editor of the website that published the letter critical of Mr Xi – Wujie News, or Watching.
He has reportedly denied he had anything to do with the letter itself.
Last week, Mr Yan told the BBC that no-one had been able to contact Mr Jia since 15 March.