Azerbaijan's independent Turan News Agency says its director has been detained by authorities as a suspect in a tax-evasion and abuse-of-power investigation.

The move on August 24 comes after the director, Mehman Aliyev, on August 18 told RFE/RL that the authorities had frozen all of the outlet's bank accounts amid a criminal probe the news agency said was politically motivated.

International rights groups decried what they called "trumped-up charges" against Turan and said they are part of a broader crackdown on independent media and critical voices in Azerbaijan.

The news outlet, which was established in 1990, publishes reports in Azerbaijani, English, and Russian and cooperates with leading international news agencies.

Turan quoted Aliyev's lawyer, Fuad Agayev, as saying the director voluntarily went to the Tax Ministry's Department of Tax Crimes office for questioning before he was detained and taken to the Yasamal district police department.

Agayev added that Aliyev’s detention was “in violation of the law.” The lawyer said Aliyev is expected to appear before the court within 48 hours, but likely not before August 25.

Officials launched a tax-evasion investigation into Turan on August 7, alleging the agency owes 37,000 manats ($21,500) in taxes for 2014-16.

Reporters Without Borders said the case was based on "trumped-up charges."

“The authorities are stepping up the pressure on Turan because they have been unable to force it to cooperate,” said Johann Bihr, the head of RSF’s Eastern Europe and Central Asia desk.

“Mehman Aliyev is one of journalism’s pioneers in Azerbaijan. His only crime is to have headed the country’s last independent media outlet. We demand his immediate release and the withdrawal of all the politically motivated charges against Turan.”

Giorgi Gogia, South Caucasus director with the New York-based Human Rights Watch, called the investigation into Turan "the latest in a vicious crackdown on critical media in the country."

Western governments and international rights watchdogs have criticized Baku for clamping down on independent media outlets, journalists, and opposition politicians and activists.

In 2014, Azerbaijan criminalized defamation on the Internet and last year it made online defamation of the president a criminal offense punishable by imprisonment.

President Ilham Aliyev, who has ruled the oil-producing South Caucasus country of nearly 10 million people since shortly before the death of his father, Heydar Aliyev, in 2003, has dismissed the criticism.

With reporting by Turan News Agency and AFP