Demonstrations swept Tunisia for a second day on Friday after the assassination of a secular opposition figure, with one protester killed and several injured in the southern city of Gafsa, witnesses said.
Late on Friday, 42 opposition members announced their resignation from the 217-seat Constituent Assembly to protest the killing on Thursday of Mohamed Brahmi, a member of the Arab nationalist Popular Front party.
Khamis Kssila of the Nida Touns party told a news conference the departing members would begin a sit-in to demand the dissolution of the assembly and formation of a national salvation government, ideas rejected by Prime Minister Ali Larayedh.
The assembly, controlled by Islamists, is in charge of drafting a new constitution for the North African nation of 11 million people.
Divisions between Islamists and their secular opponents have deepened since Tunisian President Zine al-Abidine Ben Ali was toppled in 2011 in the first of the Arab Spring revolutions.
Two witnesses told Reuters that anti-government protester Mofti Mohamed died during protests in Gafsa on Friday night. There were conflicting accounts of how he died.
There were also several people injured in Gafsa from teargas, witnesses said.
It was the first such death since protests erupted after Brahmi was shot 14 times, in the second killing of a secular politician in Tunisia this year.
Several thousand Islamists took to the streets of Tunis on Friday to defend the government from popular demands that it resign over the assassination of Brahmi.
Interior Minister Lotfi Ben Jeddou drew a direct link between the latest killing and the assassination of the Popular Front's leader, Chokri Belaid, on Feb. 6, that stoked violent protests.
Aiming suspicion at a hardline Islamist, the minister said the same gun had been used in Thursday's killing as in the Belaid assassination.
"The same 9mm automatic weapon that killed Belaid also killed Brahmi," he told a news conference, naming the main suspect as Salafist Boubacar Hakim, already being sought on suspicion of smuggling weapons from Libya.
Authorities have identified 14 Salafists suspected of involvement in Belaid's assassination, and most were believed to be members of the local hardline Islamist group Ansar al-Sharia, he said.
Islamists and secular opponents staged rival protests over the future of Tunisia's Ennahda government,
"The people want Ennahda again!" and "No to a coup against democracy!" the Islamists chanted, rejecting demands for a new government of national unity.
Thousands of anti-government protesters also massed in the capital on Friday, while shops and banks closed their doors and all flights in and out of the country were cancelled.
"Down with the rule of the Muslim Brotherhood," the secular protesters chanted, referring to the ruling Ennahda party, which draws inspiration from the Brotherhood, a pan-Arab Islamist movement.
Evening protests also erupted in the cities of Kairaouan and Kef, where police fired teargas to disperse protesters.
Brahmi, 58, was a critic of the Ennahda-led ruling coalition and a member of the Constituent Assembly.