Tunisia's hardline Salafist movement Ansar al-Sharia vowed on Thursday to go ahead with its annual congress at the weekend in defiance of a government ban on the controversial gathering.
"We are not asking permission from the government to preach the word of God and we warn against any police intervention to prevent the congress from taking place," spokesman Seifeddine Rais told a news conference in Tunis.
"The government will be responsible for any drop of blood spilt," he said, adding that more than 40,000 people were expected at the Sunday gathering, the group's third, in the historic central city of Kairouan.
Prime Minister "Ali Larayedh will answer for his policies before God," Rais said, adding that "the Salafist movement is the object of systematic discrimination."
Rais said even youths who did not belong to the Salafist movement planned to attend Sunday's meeting to "condemn the oppression."
Salafists advocate an ultra-conservative brand of Sunni Islam, and Ansar al-Sharia is considered the most radical of the extremist groups that emerged in Tunisia after the revolution.
Since the January 2011 revolution that overthrew Zine El Abidine Ben Ali, Tunisian security has been severely challenged by the rise of militant Islamists, who are blamed for a wave of violence across the country.
Thousands attended the movement's congress in 2012, some in Afghan military garb, waving swords and chanting slogans that included: "We are all children of Osama (bin Laden)," the assassinated founder of Al-Qaeda.
In recent months, the government has hardened its stance towards the extremists, after the ruling Islamist party Ennahda was heavily criticised for failing to rein them in.
The interior ministry recently made it obligatory for political parties and associations to obtain permission for all public activity.
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Ennahda leader Rached Ghannouchi said on Wednesday that the government had banned the Kairouan gathering this year because organisers did not get permission as required by law.
"The authorities must apply the law without distinction. We support the firmness of the government in applying the law for all," Ghannouchi said, while also condemning the use of violence in the name of Islam.
He revealed that Salafists had killed a Tunisian police officer earlier this month in a district in southern Tunis following a fatwa, or religious decree, issued by their imam.
The victim was slaughtered, stripped and hidden in a mosque in the Jebel Jelloud area overnight.
Ghannouchi blasted the Salafist groups for their silence over the murder.
He said violence perpetrated in the name of religion was "the worst kind," and had "no legitimacy" in Islam, signalling a shift in his party's position regarding extremist groups, with whom it previously favoured dialogue.
Separately, at the end of April the army intensified its hunt for two Al-Qaeda-linked groups of armed jihadists hiding on the border with Algeria, in an operation that has wounded at least 16 members of the security forces, some seriously.
Ansar al-Sharia's spokesman denied on Thursday any connection between his group and the jihadists being pursued by the army.
The group's fugitive leader Abu Iyadh, a former Al-Qaeda combatant in Afghanistan, is accused of orchestrating numerous acts of violence, including an attack on the US embassy last September that left four Islamists dead.
Interior Minister Lotfi Ben Jeddou, an independent in the ruling coalition, said last week that he would bring to justice "anyone inciting to murder or hatred... or who pitches tents for preaching in," in a clear reference to the radical Islamists.
At the weekend, police fired tear gas in the capital and took steps elsewhere around the country to disperse Salafist groups trying to set up tents in which to preach and disseminate their ideas.