The death of secular opposition figure Mohamed Brahmi, gunned down outside his Tunis home on Thursday, has heightened tensions in the North African country and turned up the pressure on its Islamist rulers.
Witnesses said one man was killed early on Saturday in an anti-government protest in the southern city of Gafsa. Violence also broke out in several other cities.
A bomb in a police car exploded in Tunis but caused no casualties, a spokesman at the Interior Ministry said.
Hundreds of people gathered in front of Brahmi's home in the suburb of Gazella, waving pictures of him and chanting anti-government slogans ahead of the funeral, which was starting at 9 GMT.
The funeral procession was to walk down the main street of the capital, near the Interior Ministry. Hundreds of police deployed in anticipation of violence.
Brahmi's family has accused the main Islamist Ennahda party of being behind the killing. Its leader, Rached Ghannouchi, has denounced the assassination as an attack on democracy.
Divisions between Islamists and their secular opponents have deepened since President Zine al-Abidine Ben Ali was toppled in 2011 in the first of the Arab Spring revolutions that also felled leaders in Egypt, Libya and Yemen.
Late on Friday, 42 opposition members announced their resignation from the 217-seat Constituent Assembly to protest against the killing of Brahmi, a member of the Arab nationalist Popular Front party.
Khamis Kssila of the Nida Touns party said 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 nation of 11 million people.
Several thousand Islamists took to the streets of Tunis on Friday to defend the government from popular demands that it resign over the assassination.
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, which also 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.
Tunisia's political transition since the revolt that toppled Ben Ali has been relatively peaceful, with the moderate Islamist Ennahda party sharing power with smaller secular parties.
But the government has struggled to revive the economy and has come under fire from secularists who accuse it of failing to curb the activities of Salafi Islamists.