Tunisia's anti-terrorism police detained for one day Ali Larayedh, a former prime minister and senior official in the Islamist opposition Ennahda party, after an investigation into suspicions of sending extremists to Syria, lawyers said on Tuesday.
In the same case, the police postponed the hearing of Ennahda leader and speaker of the dissolved parliament Rached Ghannouchi to midday on Tuesday, after waiting for about 14 hours.
It is expected that Larayedh will appear before a judge on Wednesday, lawyer Mokthar Jmayi told Reuters.
"We are shocked. The file is completely empty and without any evidence", Samir Dilou, another lawyer said.
Ennahda denies accusations of terrorism, calling it a political attack on a foe of President Kais Saied.
Ghannouchi, 81, has accused Saied of an anti-democratic coup since he seized most powers last summer, shutting down the parliament and moving to rule by decree, powers he has largely formalized with a new constitution ratified in a July referendum.
Last month, several former security officials and two Ennahda members were arrested on charges connected to Tunisians traveling to fight for extremist groups.
Security and official sources estimated that around 6,000 Tunisians traveled to Syria and Iraq last decade to join radical groups including ISIS. Many were killed there while others escaped and returned to Tunisia.