Police shot into the air and fired teargas on Monday to break up demonstrators protesting against Tunisia's Islamist-led government in the southern town of Sidi Bouzid, birthplace of the country's 2011 revolution.

Witnesses told Reuters that police opened fire after protesters tried to prevent the governor from entering the town hall. The secular opposition, which is trying to topple the government, has called for civil disobedience and the occupation of government offices.

Tunisia is grappling with large pro- and anti-government protests as well as a growing security threat. Islamist militants have stepped up attacks in the past two weeks and Tunisian forces launched heavy air and artillery strikes on militant hideouts near the Algerian border.

The assassination of leftist figure Mohamed Brahmi on July 25, the second killing of an opposition figure in six months, sparked the worst political crisis in Tunisia since protests toppled autocratic leader Zine El Abidine Ben Ali in 2011.

The opposition demands the dissolution of the government and the Constituent Assembly, which is just weeks away from finishing a draft constitution and a new electoral law.

Ennahda, the Islamist party that is governing in coalition with other forces, says it will negotiate on changing the government but has refused to remove the prime minister or dissolve the Assembly, which it has called its "red lines."