By Tarek Amara
TUNIS (Reuters) - A secular party in Tunisia's ruling Islamist-led coalition demanded a unity government on Monday to defuse a deepening political crisis, hours after the army sealed a square in the capital where protesters had clashed.
Tensions have been mounting over opposition efforts to oust the government following last week's assassination of a leftist politician, the second such killing in six months.
Soldiers blocked off the central Bardo square in Tunis, declaring it a "closed military zone" after pro- and anti-government protesters threw rocks at each other.
The secular Ettakatol party called for the coalition led by the Islamist Ennahda party to step down.
"We have called for the dissolution of the government in favor of a unity government that would represent the broadest form of consensus," Lobni Jribi, a party leader, told Reuters.
"If Ennahda refuses this proposal, we will withdraw from the government."
The threat by one of its own allies will ratchet up pressure on Ennahda, which has resisted opposition demands for the government's fall, and could encourage further defections.
Education Minister Salem Labyedh, an independent, has offered his resignation to the prime minister, local media said.
Tunisians fear they may be plunging into one of the worst crises in their political transition since autocratic leader Zine al-Abidine Ben Ali was forced to flee by a 2011 uprising that sparked protests across the Arab world.
Security forces sealed Bardo square, located outside the transitional Constituent Assembly, with barbed wire and fencing.
The assembly's head, Mustafa Ben Jaafar, belongs to Ettakatol. He has said it is only weeks away from completing a long-delayed draft constitution to be put to a referendum.
The secular opposition, emboldened by the Egyptian army's ousting of an Islamist president this month, is now rejecting all concessions and reconciliation efforts by the government.
It has called for the 217-member Constituent Assembly to be dissolved. In the last few days, 70 lawmakers have left the body and to set up a sit-in protest outside its headquarters.
In the southern city of Sidi Bouzid, angry protesters tried to storm municipal offices to stop employees from going to work, residents said, sparking clashes with Ennahda supporters.
The army intervened to protect the offices and police fired tear gas, but residents said thousands of demonstrators were gathering in the southern city, the cradle of Tunisia's revolt.
Opposition leaders say they might set up a rival "salvation government", an idea they will discuss later on Monday.
"DESTRUCTION OF THE STATE"
Noureddine Bhiri, a spokesman for Prime Minister Ali Larayedh, said opposition protests were tantamount to calling for "destruction of the state" at a moment when the government was trying to deal with the aftermath of the assassinations.
Bhiri challenged the opposition call for a new government, saying it had offered no vision for running the country.
"What are the alternatives that they want after dissolving the government? There is nothing but violence and destruction. We need to stay united to pass this phase and end terrorism."
Larayedh, who met the president and commanders of national security forces, was to address the nation later in the day.
France, Tunisia's former colonial power, called for restraint and said it was worried by recent events. It urged the Tunisian authorities "to see this transition through to the end, in a spirit of dialogue and respect for the roadmap".
In the fenced-off Bardo square, opposition sources said security forces had beaten one of the lawmakers who had quit the Constituent Assembly. He was taken to hospital.
"The prime minister will be held accountable for any drop of blood spilled in the Bardo sit-in," opposition figure Manji Rahawi said.
Both rival protest groups have vowed to return to Bardo despite the army takeover of the square, local media said.
Tunisia's powerful labor unions also met opposition parties on Monday and were to discuss the option of more strike action. On Friday, a strike to mourn leftist politician, Mohamed Brahmi, who was assassinated last week, paralyzed much of the country.
The government says Brahmi's assailants used the same weapon that killed another secular leader, Chokri Belaid, on February 6.
Its critics say it has not done enough to investigate or stop the attacks it has blamed on hardline Salafist militants.
Many joining the swelling street protests cite anger with the instability in Tunisia as well as economic stagnation.
Others are frustrated that a constitution, promised one year after the 2011 uprising, has yet to be completed and are suspicious of the Islamist-led transitional government.
(Additional reporting by Brian Love in Paris; Writing by Erika Solomon; Editing by Alistair Lyon)