Tajikistan on Saturday charged a BBC reporter with membership of a banned Islamist group, after his arrest sparked global concern that he was being persecuted merely for opposing the regime.
Urunbay Usmonov, a correspondent for the BBC's Central Asia service, was arrested on suspicion of membership of Hizb ut-Tahrir, which is outlawed in the secular Muslim states of ex-Soviet Central Asia.
A criminal investigation has been opened against him "for participation in an extremist group," the Tajik state committee for national security told AFP in a statement.
"The initial investigation, based on witness testimony and evidence, confirms Usmonov's membership in Hizb ut-Tahrir," it said.
It added that Usmonov allegedly had long maintained contact with Hizb ut-Tahrir figures and distributed its materials with the aim of bringing about a "violent seizure of power and change in the constitutional makeup of Tajikistan."
The BBC, which gives Usmonov's age as 59, has said it "has no reason to believe these allegations" and also noted that Usmonov's family has said he appeared to have been beaten up by the Tajik security services.
The British embassy has urged Dushanbe to clarify the situation while the Organisation for Security and Cooperation in Europe has said his arrest "raises concerns about undue limitations on free expression."
Global media rights watchdog Reporters Without Borders said there is "little doubt" that Usmonov was arrested for his journalistic activities, noting that he has been unafraid to report on sensitive subjects like Tajikistan's controversial Rogun Dam project.
"Using the fight against extremism in order to crack down on dissidents is standard practice in Tajikistan," it said in a statement. "So far, it is the police who have behaved illegally in this case."
Freedom House meanwhile called for Usmonov's immediate release, saying the Tajik authorities "have a history of using the fight against extremism as an excuse to crack down on voices of dissent."
Usmonov has worked for the last decade for the BBC's Uzbek-language operation. Turkic-speaking Uzbeks form the largest minority in Tajikistan, whose national language is derived from Persian.
Hizb ut-Tahrir was founded in the 1950s in the Middle East and advocates the establishment of an Islamic "caliphate" across Muslim Central Asia, although its members insist they believe this should be achieved by peaceful means.
It appeared in Central Asia around a decade ago and its attempts to recruit new members and its distribution of anti-government literature has worried the authorities, particularly in Tajikistan, the poorest state of the former Soviet Union.
In the past decade, Tajikistan has convicted some 500 men and women for membership of Hizb ut-Tahrir. This year alone, 40 have been jailed.
The Tajik authorities led by President Emomali Rahmon fought militants in a civil war after the collapse of the Soviet Union and last summer the country saw a new spate of militant attacks in the restive Rasht Valley.
The Tajik defence ministry at the time accused some local media of effectively supporting the militants with their coverage and blocked access to leading news sites.