TUNIS - Tunisia's Islamist-led government discussed ways to ease political tensions at an emergency meeting Monday as protests mounted demanding its ouster and police clashed with stone-throwing demonstrators in Sidi Bouzid.

"The council of ministers discussed several alternatives and will announce adequate measures at 5:00 pm (1600 GMT) after more consultations with its coalition partners," Noureddine Bhiri, political adviser to Islamist Prime Minister Ali Larayedh, told reporters. A government minister earlier said "important decisions" would emerge from the meeting.

As soon as the cabinet meeting was over, Larayedh headed to a security meeting chaired by President Moncef Marzouki.

Tensions have frayed across Tunisia, particularly in Sidi Bouzid, cradle of the 2011 Arab Spring popular uprising that toppled strongman Zine El Abidine Ben Ali, and home town of an anti-Islamist MP who was assassinated on Thursday.

Mohamed Brahmi was the second opposition politician killed after Chokri Belaid was gunned down outside his home in February and many Tunisian blame the govt for both killings. Government detractors say the Ennahda-led cabinet has failed to rein in radical Islamists who have grown in influence and stand accused of a wave of attacks since the 2011 uprising. The 500,000-member General Union of Tunisian Labour (UGTT) was also due to meet in the evening "to decide the fate" of the country, its secretary general Sami Tahri said.

"The UGTT will carry out its historic role to defend the right of Tunisians to protest peacefully... and assume its responsibilities vis-a-vis the crisis as it did on January 14 (2011)," Tahri said, referring to the date when the powerful union joined the uprising against Ben Ali. On Monday morning, anti-government  rotests erupted in both Tunis and Sidi Bouzid, with demonstrators demanding the resignation of the government and the dissolution of parliament. In both cities, police used tear gas to disperse the protesters, AFP correspondents reported. In the centre-west city of Sidi Bouzid, they fired tear gas to disperse stone-throwers among a crowd of hundreds of protesters who blocked employees from going to work at the governor's office.

"Ghannouchi, assassin!" the crowd chanted in reference to Ennahda party leader Rashid Ghannouchi.  Demonstrators demanded the dismissal of the governor, who is regarded as close to the Islamists. In Tunis, police fired tear gas to disperse protesters rallying outside the National Constituent Assembly for a fourth day running. Overnight around 10,000 people demonstrated for and against the government on Bardo Square outside the parliament building, separated by police vans and metal barricades.

Protests have swelled at night in Tunis, where streets are empty during the day because of searing temperatures and the dawn-to-dusk fast observed by the faithful during the Muslim holy month of Ramadan.

Protesters chanted: "The people want the fall of the assassins," while across the barricades government supporters retorted: "The people are Muslim and will not capitulate".

"Those who boycott the NCA betray Tunisia," Ennahda MP Fathi Ayadi told AFP.

NCA speaker Mustapha Ben Jaafar has called for "restraint" and urged deputies to return and resume work on a much-delayed constitution, one of the thorniest issues in post-revolution Tunisia.

Dozens of MPs have been boycotting parliament since Brahmi's murder.

Authorities have accused radical Salafists close to Al-Qaeda-linked group Ansar al-Sharia of gunning down Brahmi, whose body was riddled with 14 bullets outside his home.

They say the same gun was used to assassinate Belaid in February.

Ansar al-Sharia denied any responsibility. It said in an online statement that Brahmi's murder was political and "only profits remnants of the former regime and lackeys of the Zionists and Crusaders".

Hundreds of thousands of mourners thronged the streets of Tunis on Saturday for an emotionally charged funeral procession to El-Jellaz cemetery, where Brahmi was buried next to Belaid.

Slogans vowing to "avenge" the two slain oppositionists rose from the sea of mourners.

Anti-government protesters then assembled outside the NCA and clashed with police, who fired tear gas to disperse them. An opposition MP suffered a blow to the head, AFP correspondents reported.

Interior Minister Lotfi Ben Jeddou has since pledged to guarantee the safety of anti-government demonstrators, leftist MP Samir Taieb said after meeting the minister.

Taieb, who has been calling on the government to step down and hand over to a national unity administration, said nearly a third of the 217 members of the assembly were boycotting its sessions.