Tunisia's national prevention of torture body said authorities have not provided any information on the arrest of former deputy president of the Ennahda party.
Appeals have mounted for word on the whereabouts of detained Tunisian politician Noureddine Bhairi, a leader of the Ennahda party, the largest in the North African country's suspended parliament.
Plain-clothes officers arrested Bhairi, a former justice minister and deputy president of Ennahda, in the capital Tunis on Friday.
Tunisia's independent national body for the prevention of torture (INPT) said in a statement that authorities had provided no information on Bhairi nor on Fathi Baldi, a former interior ministry official who was also taken in for questioning on Friday.
The body's president, Fathi al Jarray, said there had been "no response" from the interior ministry to its requests for information about the two men.
Lawyer and INPT official Lotfi Ezzedine said that some individuals had been placed under house arrest over the summer, but "this is even worse because we don't even know where they are detained".
Bhairi and Baldi were "neither in an official detention facility, nor at their homes, nor at a police station", he said, charging that the pair's location was being "kept secret".
Ezzedine said the interior ministry had ordered the pair under preventive detention without legal proceedings because they allegedly presented "'a danger to public order'."
Ennahda denounces 'kidnapping'
Ennahda said on Friday that authorities were questioning Bhairi and denounced "a kidnapping and dangerous precedent marking the country's entry into a tunnel to dictatorship".
Ennahda party lawmaker Habib Khedher said Interior Minister Taoufik Charfeddine had refused on Saturday to meet with representatives of Bhairi's defence committee.
He said Bhairi's wife Saida Akremi and the head of the national order of lawyers had requested a meeting to check on the health of Bhairi, who suffers from several chronic illnesses.
Tunisia was the only democracy to emerge from the Arab Spring revolts of a decade ago. But civil society groups and President Kais Saied's opponents have expressed fear of a slide back to authoritarianism a decade after the revolution that toppled longtime ruler Zine El Abidine Ben Ali.
Ennahda had played a central role in the country's politics until the power grab by Saied in July.
Saied sacked the Ennahda-supported government and suspended parliament on July 25, presenting himself as the ultimate interpreter of the constitution.
He later took steps to rule by decree, and in early December vowed to press on with reforms to the political system.