TUNIS, Feb 19, 2011 (AFP) - Hundreds of Tunisians demonstrated Saturday for a secular state following the murder of a Polish priest, verbal attacks on Jews and an attempt by Islamists to set fire to a brothel.

Rallied by a call on social network Facebook, they gathered in the main Avenue Bourguiba in Tunis waving placards reading, "Secularism = Freedom and Tolerance" and "Stop Extremist Acts".

"We've called this demonstration to show that Tunisia is a tolerant country which rejects fanaticism and to strengthen secularism in practice and in law," blogger Sofiane Chourabi, 29, said.

Police stood by as military helicopters circled overhead.

The 34-year-old priest Marek Rybinski was found dead Friday with his throat slit in the garage of a private religious school at Manouba near the capital where he was responsible for the accounting.

"To kill a Catholic in Tunisia is abnormal and to commit this crime in these circumstances is abnormal. These indications show us that this is a crime committed by extremists," a government official said.

Police and army "will rigorously fight and without hesitation all acts against religion because it is Tunisia's image that is at stake," the official added.

Some protestors said ousted President Zine El Abidine Ben Ali's henchmen may have carried out the murder in order to sow chaos and as propaganda to show that the new Tunisia is intolerant.

"To cut someone's throat, it's not the habit of Tunisians," said 42-year-old Kaouther.

Ben Ali's authoritarian regime presented itself as a bulwark against fanaticism, jailing thousands of Islamists in the 1990s.

Tunisia's bishop Lahham Maroun meanwhile said he was invited to meet with Prime Minister Mohamed Ghannouchi on Sunday when a funeral service for Rybinski will be held.

The priest in charge of the school, Mario Mulestagno, revealed Saturday that it had received a death threat at the end of January in a confused letter stamped with a swastika and addressed to "the Jews".

The main Islamist movement in Tunisia, Ennahda (Awakening), also "strongly" condemned the murder Saturday, saying it was "a tactic to distract Tunisians from the objectives of Tunisia's revolution."

"We denounce what happened and we condemn all those who are behind it. We call on the Tunisian authorities to discover the real circumstances of this murder and find the people who did it to enlighten public opinion," the president of the movement's founding assembly, Ali El-Aryath, said.

The murder was the first of a foreigner or priest since Ben Ali's was toppled by mass protests on January 14. An interim government has been installed but the situation in the country is still extremely volatile.

The priest's body was found as hundreds of Islamists rallied in Tunis Friday calling for the closure of brothels in the city. A march on a street housing one of the best-known brothels was thwarted by police.

Anti-Jewish slogans were shouted outside the main Tunis synagogue earlier this month.

Meanwhile a general amnesty for thousands of political prisoners held under Ben Ali's regime came into force Saturday, the state news agency TAP said.

Elsewhere some 500 Tunisians rallied outside the French embassy condemning newly-appointed ambassador Boris Boillon protesting at remarks they deemed insulting and calling for his departure.

While calling for a "new page" in relations between France and Tunisia, Boillon, 41, refused to take questions from some journalists at a press conference on Thursday and dismissed others as "stupid".

Late Saturday he went on national television to apologise to journalists and the Tunisian people and expressed his regrets that his remarks had appeared "arrogant".

France, the former colonial power, failed to realise the strength of the opposition to Ben Ali and Foreign Minister Michele Alliot-Marie is under pressure to resign over her links to the deposed regime.