Tunisian protesters clash with riot police during a demonstration near the parliament building in Tunis on Saturday. Tunisian police fired tear gas in front of parliament to disperse secular protesters demanding the dissolution of the assembly and Islamists defending the legitimacy of their rule. Zoubeir Souissi / Reuters

Protests against Tunisia's Islamist-led government erupted Saturday as thousands thronged the streets of the capital for the funeral of an assassinated leftist opposition leader, the second such killing since February.

Demonstrators calling for the fall of the government marched on the National Assembly in central Tunis and clashed with riot police, who fired tear-gas to disperse them, an AFP correspondent said, adding that an opposition MP was injured by a blow to the head.

Mohamed Brahmi was shot dead on Thursday outside his home in a Tunis suburb, and authorities said he was killed with the same gun used in the murder of leftist politician Chokri Belaid in February.

Brahmi's coffin, draped in the red-and-white Tunisian flag, was saluted by soldiers as the cortege left from his home for El-Jellaz cemetery.

Emotions ran high as supporters of Brahmi, including family members, lifted the coffin to their shoulders before placing it on a military vehicle under armed escort.

A military helicopter flew over the capital as flags fluttered among the crowd waiting for the funeral procession along Habib Bourguiba Avenue, epicenter of the 2011 Arab Spring born in Tunisia.

Slogans vowing to "avenge" Brahmi rose from the sea of mourners.

Police deployed reinforcements for the funeral attended by some 10,000 mourners, according to official estimates. Journalists gave a higher figure of between 15,000 and 20,000.

"Allahu akbar! (God is great). There is no God but Allah, and martyrdom is his friend," mourners cried out at the cemetery.

Army chief of staff General Mohamed Salah Hamdi read the eulogy and an imam prayed. There were no representatives from the ruling Islamist Ennahda party, which the family blames for Brahmi's killing.

His widow Mbarka, who wore a headscarf, made the V-for-victory sign.

"The people want the fall of the regime," and "Ennahda terrorist gang," the crowd shouted, before falling silent for the national anthem.

The coffin was then lowered into a grave in the "martyrs'" section of the cemetery next to that of Belaid, in accordance with his wishes.

Brahmi, 58, was killed with the same weapon used to gun down Belaid, Interior Minister Lotfi Ben Jeddou said on Friday.

The state prosecutor's office said an autopsy found Brahmi had been hit by 14 bullets and authorities blamed extremists with links to al-Qaida.

His murder has stoked tensions in Tunisia, where many blame the government for failing to rein in radical Islamists accused of a wave of attacks since the regime of strongman Zine El Abidine Ben Ali was toppled in a popular uprising in 2011.