Reuters have filed a report from the funeral of Mohamed Brahmi in Tunis.

Tens of thousands of Tunisians turned out for the funeral of assassinated secular politician Mohamed Brahmi and called for the Islamist-led government to be toppled.

Military helicopters hovered overhead and hundreds of troops and police lined the route of a procession attended by Brahmi's widow and son and several prominent politicians.

"The people want to topple the regime!" and "With our blood and with our souls we will sacrifice ourselves for the martyr!" people in the crowd shouted.

"Ghannouchi, assassin, criminal," others chanted, referring to Rached Ghannouchi, leader of the ruling Islamist Ennahda party that Brahmi's family says was behind the killing.

The death of secular opposition figure Brahmi, gunned down outside his Tunis home on Thursday, came months after another secular leader, Chokri Belaid, was killed in a similar attack that stoked violent protests.

Interior Minister Lotfi Ben Jeddou drew a direct link between the latest killing and the assassination of the Popular Front's leader Belaid.

Aiming suspicion at a hardline Islamist, the minister said the same gun had been used in Thursday's killing as in the Belaid attack.

"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.