Former Tunisian prime minister, Ali Larayedh, has been detained by anti-terrorism police over his alleged involvement in smuggling of jihadists to Syria.
According to reports, a senior figure in the Islamist opposition Ennahda party Mr Larayedh had been questioned for hours as well.
Ennahda in a statement denounced this action as a flagrant violation of human rights.
Prty leader Rached Ghannouchi is due to be questioned later on Tuesday.
Ennahda rejects the charges.
President Kais Said has tightened his grip on the judiciary following his suspension of the Ennahda-dominated parliament last year.