Violent protests broke out in the Tunisian town of Sidi Bouzid, the birthplace of the uprising that ousted Zine el Abidine Ben Ali, after election results were announced Thursday, witnesses and the government said.

More than 2,000 young people marched on the headquarters of the Islamist Ennahda party, the election victor, and pelted security forces with stones after they learned that another political grouping's candidates' lists were invalidated, said the witnesses and the interior ministry.

"A violent protest is under way, the security forces are trying to contain it," ministry spokesman Hichem Meddeb told AFP.

An AFP correspondent reported that the group broke doors and windows of the Ennahda building and set alight tyres on the town's main road.

A similar protest was under way in the town of Regueb, some 50 kilometres (30 miles) from Sidi Bouzid, said witnesses, where a gunshot was fired at the local Ennahda offices.