The Chadian authorities on Monday detained a journalist on charges of "threatening constitutional order", his lawyer and colleagues said.
Eric Topona, secretary-general of the Union of Chadian Journalists (UJT), was "summoned as a witness in a defamation case" and subsequently detained, his lawyer Sobdibe Zoua told AFP.
"The UJT is saddened to learn that its secretary-general Eric Topna was arrested Monday and detained at the N'Djamena detention centre," union chairman Mahamd Moussa Abba said.
He claimed the arrest was linked to that on March 22 of Jean Etienne Laokole. Both journalists contributed to a blog edited by a foreign-based Chadian who is critical of President Idriss Deby Itno's regime.
The Paris-based watchdog Reporters Without Borders called for Topona's immediate and unconditional release.
"The arrest and charging of Topona, who has been harassed several times in the past in connection with his journalistic activities, are unacceptable and constitute a flagrant violation of freedom of information," it said,
The arrest comes amid renewed political tension in the chronically unstable country, where the government said it foiled a coup plot last week.