Tunisian Salafist group Ansar al-Sharia, which the government has branded a terrorist organisation, has called for a protest in the central city of Kairouan on Friday against the arrest of its spokesman.
"Call to all Muslims to a protest in support of Ansar al-Sharia's spokesman Seifeddine Rais, in front of the headquarters of ruling Islamist party Ennahda near Bab Jalladine" in Kairouan, the group said on its Facebook page.
Rais was arrested on Sunday in Kairouan where the Salafist group had planned to hold an annual congress that was banned by the authorities.
The interior ministry swiftly responded to Ansar al-Sharia's call to protest by stating that unauthorised public demonstrations were prohibited.
"The organisation of demonstrations in public places requires a request for permission from the authorities concerned, who must be alerted three days in advance," the ministry said.
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It has not given a reason for Rais's arrest, carried out at dawn as he was jogging in Kairouan, with ministry spokesman Mohamed Ali Aroui simply saying: "The law will be applied when a person fails to respect the law."
Following the ban on Sunday's planned congress, and a heavy deployment of security forces in Kairouan to enforce it, Ansar al-Sharia told its members to rally instead in the Tunis suburb of Ettadhamen.
Clashes erupted when police moved into the Salafist stronghold, with at least one person killed and 18 people wounded in the violence, including 15 policemen.
The Salafists, who advocate an ultra-conservative brand of Sunni Islam, were initially tolerated by the authorities following Tunisia's January 2011 revolution, even as a wave of violence linked to the extremists swept the country.
The attacks have targeted art galleries, cultural festivals and Sufi shrines, and culminated last September in an assault on the US embassy that left four Islamists dead.
But faced with the threat of Al-Qaeda-linked jihadist groups along its western border, the government has since hardened its stance towards Ansar al-Sharia, considered the most radical of the extremist groups to have emerged since the revolution.