Artists and opposition media accuse the Islamist-led government of failing to do more to rein in the Salafists, who attacked the Bizerte music and theatre festival on Thursday evening armed with swords and sticks.
The interior ministry said that five people were wounded in the attack, and that police dispersed the assailants with tear gas, arresting four of them.
But some complained that police waited an hour before intervening.
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It was the third and and most violent such incident in just three days, after Salafists prevented an Iranian group from performing at a Sufi music festival in Kairouan, south of Tunis, saying their Shiite chanting amounted to a violation of Islamic values.
On Tuesday, renowned Tunisian actor Lotfi Abdelli was prevented from performing his comedy act "100% Halal" by hardline Islamists who had occupied the auditorium.
So far the incidents have not triggered wider violence, as happened when suspected Salafists attacked a Tunis art gallery in June, sparking riots that left one person dead and more than 100 injured.
But since then, emboldened hardliners have disrupted at least five cultural events, in the middle of the festival season and during the Muslim holy month of Ramadan, heightening concerns in Tunisia about their influence and ability to operate.
Last week, the director of a festival at Gboullat, in the northern Beja region, announced he was cancelling the event under pressure notably from the Salafists -- adherents of a strict Sunni interpretation of Islam similar to the one practised in Saudi Arabia.
Another festival had been cancelled at the end of July, in Sejnane, with the organisers again blaming radical Islamists, who interrupted the event, saying it was unacceptable during the month of Ramadan.
No group has yet claimed responsibility for the disruption. The main Salafist organisation, Ansar al-Sharia, refuses all contact with the media.
RULING ISLAMIST PARTY BLAMED
The security forces have been swift to disperse anti-government protests in recent weeks but have appeared softer towards the Islamists, according to some, prompting accusations of complicity against the ruling Islamist party Ennahda.
"They leave the Salafists alone," said Tunisian actress and playwright Leila Toubel.
"How can we believe that this government and Ennahda are not involved? I would like to think that there is nothing to it, but these people (the Salafists) go unpunished, they make their own law," Toubel said.
She accused the ruling Islamists of "complicity at least by silence."
Some Tunisian media share her concerns.
"What is serious about all this, more than the activism of these religious extremists, which grows by the day, is the laxity of the authorities who give in every time when faced with the diktats of some bearded fanatics," said the online publication Kapitalis, which is strongly critical of the government.
The interior ministry declined immediate comment.
But the culture ministry responded to the forced cancellation of Lotfi Abdelli's stand-up comedy show by accusing those responsible of an "attack on freedom of expression and a dangerous threat to cultural rights."
Ennahda is already under fire from human rights activists for drafting a law, yet to be debated in parliament, that could see anyone convicted of violating religious values jailed for up to two years.
Critics say the bill is an attempt to curb freedom of expression.
