Tanzania on Friday charged the co-founder of a website where people can post comments on officials they believe are corrupt with offences including obstructing a police investigation.
Maxence Melo Mubyazi was arrested on Tuesday and has since been held by police, who have also searched his office and home.
A charge sheet seen by Reuters showed that Mubyazi, 40, managing director and co-founder of jamiiforums website, has been charged with multiple counts of obstructing justice and running a website that is not registered in Tanzania.
At his court appearance on Friday in Tanzania's commercial capital Dar es Salaam, he denied the charges and was returned to custody after an unsuccessful bail application.
According to the charge sheet, Mubyazi had been aware police were conducting a criminal investigation of the content on his website but, "with intent to obstruct investigation, did unlawfully fail to comply with an order of disclosure of data in his possession".
The catchphrase of the jamiiforums website is "where we dare to talk openly". Most users post their comments under pseudonyms.
The site's managers have denied accusations by officials that it allows users to post fabrications and seditious content.
Last year the east African country enacted a tough cybercrimes law under which several people have been prosecuted for violations including insulting the president, which is punishable by up to three years in jail.
Rights activists have criticized the law, and the United States has cancelled nearly $500 million of funding for the country to express its disapproval.
Tanzania's President John Magufuli has won some praise from western donors for an anti-corruption drive and cutting wasteful public spending. Opponents accuse him of undermining democracy by curbing dissent and stifling free speech.
Pressure group the Committee to Protect Journalists said in a statement this week Tanzania should investigate corruption allegations instead of "pressurizing a website to violate its users' trust and privacy".