Troops patrolled the streets of the Tunisian capital after an overnight curfew, as the government tried to quell weeks of violent protests and fend off mounting international criticism of its crackdown.
The government of President Zine El Abidine Ben Ali reacted by sacking its interior minister on Wednesday and pledging a commission to investigate corruption in the tightly controlled North African country.
The opposition said sacking the interior minister, after the police force was roundly condemned for opening fire on demonstrators, fell far short of the "deep reforms" required.
"Tunisia needs global reform as well as the formation of a national unity government more than ever," to deal with the crisis, Progressive Democratic Party (PDP) secretary general Maya Jribi said.
The statement came as weeks of protests over rising food prices and unemployment reached the capital and security forces fired tear gas to disperse hundreds of demonstrators in the city.
A new government would fight corruption, guarantee judicial independence, and pave the way for early legislative elections under the control of an independent organism, Ms Jribi said in a statement.
He called for a constitutional amendment "to guarantee a peaceful handover of power" and reestablish security "so as to avoid chaos".
The government ordered the dusk-to-dawn curfew in Tunis citing "disturbances, pillaging and attacks against people and property which have occurred in some districts of the city".
Soldiers deployed in the capital were there "solely to protect public institutions against acts of vandalism and looting," Prime Minister Mohamed Ghannouchi said.
Fresh clashes were reported Wednesday in the towns of Douz, 550 kilometres (340 miles) south of Tunis — where witnesses said two people were killed after police fired on protesters — as well as Thala and Sfax.
Labour activists say security forces have killed more than 50 people in a crackdown on demonstrations, mainly in the western Kasserine region when weeks of protests in the interior escalated into deadly violence.
The government says that 21 people were killed.
UN High Commissioner for Human Rights Navi Pillay expressed concern about the "very high number of people killed".
"It is imperative that the government launch a transparent, credible and independent investigation into the violence and killings," she said, adding that members of the security forces should be punished if found guilty of excesses.
The Police on Wednesday also detained a Communist party leader, his wife said, making him the first politician arrested since the unrest began.
Hamma Hammami, the leader of the Tunisian Workers' Communist Party (POCT), which is banned by the government, was arrested at his home near Tunis, Radia Nasraoui told AFP.
The 59-year-old has repeatedly denounced Ben Ali's government to foreign media.