UPDATE 4-Tunisian Salafi Islamists riot over "insulting" art

* Some of worst clashes since overthrow of Ben Ali

* Piles pressure on government led by moderate Islamists

* Islam has emerged as most divisive political issue

(Adds interior ministry statement, curfew, clashes in Sousse)

TUNIS, June 12 (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."

DIFFICULT POSITION

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 northwestern 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)