TUNIS (Reuters) - Thousands of Salafi Islamists, angered by an art exhibition they say insults Muslims, rampaged through parts of Tunis on Tuesday, raising religious tensions in the birthplace of the Arab Spring and piling pressure on the moderate Islamist government.
Protesters hurled rocks and petrol bombs at police stations, a court house and the offices of secular parties in some of the worst clashes since last year's revolt ousted President Zine al-Abidine Ben Ali and launched uprisings across the Arab world.
Salafis, who follow a puritanical interpretation of Islam, blocked streets and set tyres alight in the working class Ettadamen and Sidi Hussein districts of the capital overnight.
By morning, protests had spread to a number of residential districts in the capital and to other cities, posing one of the biggest threats yet to Tunisia's democratic transition.
Stone-throwing youths stopped trams from passing through the capital's Intilaqa district where demonstrators entered mosques and used the loudspeakers to call on Tunisians to defend Islam.
Some 2,500 Salafis were still clashing with police in the area by Tuesday evening, an interior ministry official said, adding that 162 people had been detained and 65 members of the security forces had been wounded trying to quell the riots.
The interior and defence ministries imposed a night time curfew on the capital and seven other areas after Interior Minister Ali Larayedh told parliament he expected the riots to continue in the coming days, stretching security forces.
The clashes came a day after the Spring of Arts exhibition in the upscale La Marsa suburb provoked an outcry from some Tunisians who say it insulted Islam. The work that appears to have caused most fury spelt out the name of God using insects.
"These artists are attacking Islam and this is not new. Islam is targeted," said a youth, who gave his name as Ali and had removed his shirt as he prepared to confront police in Ettadamen. "What added fuel to the flames is the government's silence," said Ali, who did not describe himself as a Salafi.
Officials of the Islamist-led government have condemned the art works that they say were intended to insult and provoke, but said there was no excuse for the outbreak of violence that appeared planned and coordinated and could undermine economic recovery as the tourism and harvest seasons get underway.
Larayedh vowed the police would confront any more acts of violence, which he blamed on a mix of violent Salafis, criminal gangs and Ben Ali loyalists seeking to undermine the revolution.
"We have entered a phase in which we may see similar incidents and expect it to continue in the coming days and for the number of arrests to increase," he told parliament.
"These groups will not succeed no matter what they do... We will confront those that attack national security."
The violence has raised tough questions about the limits of freedom in the new Tunisia and fuelled fears among Tunisians of a slide into instability. It has also put the ruling moderate Islamist party Ennahda in a tough position as it struggles to satisfy conflicting demands.
While Islamists did not play a major role in the revolution, the struggle over the role of Islam in government and society has since emerged as the most divisive issue in Tunisian politics and several clashes have erupted in recent months, some of them involving attacks on alcohol vendors.
Salafis, some of whom are sympathetic to al Qaeda, want a broader role for religion in the new Tunisia, alarming secular elites who fear they will seek to impose their views and ultimately undermine the nascent democracy.
Some secularists had attended the offending exhibition, saying Tunisians had the right to artistic freedom, and they have also come under physical attack.
A labour union office in the north-western city of Jendouba had been set alight by Salafis overnight while the offices of secular parties nearby were attacked, Larayedh said, in an apparent effort to inflame tensions that are already bubbling between the Islamist-led government and the secular opposition.
Clashes also broke out in the coastal city of Sousse, where an art centre came under attack by Salafis. A secular party came under attack in the border town of Tataouine and protesters blocked the road from Tunis to the city of Bizerte, 60 km away.
Larayedh said the violence appeared organised and some of it may have been inspired by a recent statement from al Qaeda leader Ayman al-Zawahri, rather than simply an art exhibition.
On Sunday, Zawahri called on Tunisians to defend Islamic law from Ennahda, which won the first post-revolutionary election in North Africa in October and has said it would not seek to impose sharia in the new constitution that is being drawn up.
The audio recording, released on Islamist websites, said Ennahda, which leads Tunisia's government in coalition with two secular groups, had betrayed the religion.
Secularists say Ennahda has been too lenient with Salafis, many of whom were jailed on terrorism charges before the revolution, giving them the confidence to step up their demands.
(Additional reporting by Mohammed Argouby, Writing by Lin Noueihed; Editing by Andrew Heavens and Roger Atwood)