Ammon News - TUNIS (Associated Press) - Gunmen killed at least eight Tunisian soldiers Monday, staging the biggest attack on the security forces in decades as political tensions rose between supporters and opponents of the Islamist-led government.

State television called the ambush on Mount Chaambi, near the Algerian border, a “terrorist attack.” Tunisian troops have been trying to track down Islamist militants in the remote region since December last year.

President Moncef Marzouki announced three days of mourning, state TV reported. It cut off normal programming to pictures of the dead soldiers and wounded comrades, broadcasting Quranic verses and patriotic anthems in the background.

Tunisians fear they may be sliding into one of the worst crises in their political transition since autocratic leader Zine al-Abidine Ben Ali was forced to flee during a 2011 uprising that set off revolts across the Arab world.

Instability has been rising during the political chaos. Last week, the capital Tunis was hit by its first ever car bomb, though no one was hurt.

After clashes between pro- and anti-government protesters Monday, the army sealed off the main Bardo square in the capital with barbed wire and declared it a “closed military zone.” Demonstrators on both sides vowed to return in the evening.

The secular Ettakatol party, a junior coalition partner, called on the moderate Islamist Ennahda party which leads the government to step down, saying a new administration representing a wider consensus was necessary. “If Ennahda rejects this proposal, we will withdraw from the government,” Lobni Jribi, a party leader, told Reuters.

Prime Minister Ali Larayedh ignored the calls to a new unity government and said he would carry on leading the country.

Protests aimed at ousting the government intensified last week after the second assassination of a politician from the secular opposition in six months. The government blamed hard-line Salafist militants for both attacks, but the opposition holds Ennahda responsible, arguing that its leadership has not done enough to investigate and crack down on militant attacks.Despite previous unrest, Tunisia had been a model for democratic transition among the “Arab Spring” states. But divisions are growing between the opposition – emboldened by the Egyptian army’s ousting of elected Islamist president Mohammad Morsi – and Ennahda supporters, who are determined to avoid a similar fate.

The opposition may be able to mobilize Tunisians further against the government after Monday’s ambush which shocked the country and increased anti-government sentiment on social media.

This week the opposition rejected all concessions and efforts at reconciliation by Ennahda, arguing that its leaders bumbled for too long and that their time was up. It is planning to its own rival “salvation government.”

Tunisia’s powerful General Union of Tunisian Workers was in talks with the opposition Monday, and has said it may discuss a strike. Last Friday, its strike called to mourn the assassinated leftist politician, Mohammad Brahmi, paralyzed much of the country.

Prime Minister Layaredh struck a note of defiance in a speech on Monday, calling the opposition protesters “coupists.”

He also challenged his critics to act constructively.

“We are open to all kinds of dialogue with all sides. We want specific proposals,” he said. “Any precise suggestions regarding increasing the effectiveness of the government, bring them forward.”

A Constituent Assembly is only weeks away from completing a long-delayed draft constitution to be put to a referendum. The secular opposition has called for the 217-member Assembly to be dissolved. In the last few days, 70 lawmakers have left the body and set up a sit-in protest outside its headquarters.