Tunis: Tunisia's Islamist Ennahda party on Friday got to work on forming a coalition government after winning a strong mandate in the Arab Spring's first elections.

But as victory celebrations were underway, its offices in Sidi Bouzid, the birthplace of the Tunisian revolution, were targeted by youths upset after candidates belonging to rival party were disqualified by election authorities.

Late-night results showed Ennahda, banned under dictator Zine el Abidine Ben Ali, took 90 of the 217 seats, or 41,47 percent, in an assembly that will rewrite the constitution and appoint a president and a caretaker government.

The historic polls nine months after Ben Ali's ouster, saw the Congress for the Republic (CPR) and Ettakatol emerge as the biggest parties on the splintered left, with 30 and 21 seats respectively. Both have said they were in coalition talks with Ennahda.

Fourth place, or 19 seats, went to the Petition for Justice and Development, a grouping of independents led by Hechmi Haamdi, a rich London-based businessman said to have close ties to Ben Ali.

This despite the invalidation of six of its candidates lists, including those in Sidi Bouzid in central Tunisia. Haamdi later withdrew from the assembly in protest.

The invalidation announcement triggered violent protests in Sidi Bouzid, where an unemployed university graduate set himself on fire in December and sparked the Tunisian uprising that launched region-wide revolts.

Large crowds marching on the Ennahda party headquarters in the town overnight where they threw stones at police and burnt tyres in the street, witnesses and officials said.

Several public buildings were vandalised but calm had returned by the early morning hours though schools, public buildings and businesses remained closed.

Ennahda's offices, a municipal building and a local court were damaged in the unrest, and administrative files burnt, interior ministry spokesman Hichem Meddeb said.

Ennahda's number two and prime ministerial candidate Hamadi Jebali, meanwhile said: "I thank God for this victory. We are on the road of glory.

"Thank you to our martyrs. I bow before their sacrifice, and salute our competitors and those who did not vote for us," he said on national television after the announcement of the vote tally.

"The results of a big test," La Presse daily wrote, adding: "Tunisians voted poorly for modernists and liberals."

The CPR and Ettakatol, while secular in their constitutions, have insisted on Tunisia's Muslim identity and did not run anti-Ennahda campaigns like some of the other parties on the left, pointed out La Presse.