Tunisian police on Thursday arrested former prime minister Hamadi Jebali, an ex-senior figure in the Ennahdha party which is the nemesis of current President Kais Saied, Jebali's lawyer said.
He could not say why Jebali was detained.
"The police arrested Mr Jebali in his car in Soussa, then took him to Tunis," Zied Taher said.
For more than a month, Jebali has been under investigation over activities at his boiler factory in Soussa, a coastal city south of the capital, Taher said.
The arrest comes with civil society and Saied's opponents fearing a slide back to the authoritarianism seen under long-time dictator Zine El Abidine Ben Ali, toppled in a 2011 revolution.
Ennahdha was the dominant force in a parliament dissolved by Saied after he sacked the government and seized wide-ranging powers last July.
PAY ATTENTION: Share your outstanding story with our editors! Please reach us through email@example.com!
Private radio station Mosaique FM said Jebali had been remanded in custody by anti-terrorist police "on suspicion of money-laundering".
Jebali led the Tunisian government from December 2011, a year after the start of the country's revolution, until his resignation in early 2013 following the murder of leftist activist Chokri Belaid.
In 2014 he quit politics and left Ennahdha.
A solar engineer and former journalist, Jebali was sentenced to 16 years behind bars under Ben Ali as anti-Islamist repression intensified.
He served a large part of his sentence in an isolation cell before being pardoned in 2006.