Ammon News - TUNIS (Reuters) - Tens of thousands of Tunisians came out in a of force for the country's Islamist-led government on Saturday, in one of the largest demonstrations since the 2011 revolution.

Supporters of the ruling Ennahda party crowded into Kasbah Square next to the prime minister's office in the capital, Tunis. Ennahda officials said more than 150,000 attended. Fireworks flashed overhead and red Tunisian flags fluttered over a sea of demonstrators.

"No to coups, yes to elections," the crowd shouted, in a reference to the army-backed ouster of Egypt's elected Islamist president last month.

The secular opposition is stepping up efforts to oust the transition government in the North African country. At the same time, security forces are struggling to fight off a spike in attacks by radical Islamist militants, whom the moderate Islamist Ennahda has condemned as terrorists.

The country, once considered a model among fledgling "Arab Spring" democracies, is facing its worst crisis since Tunisians toppled autocrat Zine el-Abidine Ben Ali and set off a wave of uprisings across the region.

The opposition, angered by the assassination of two of its figures and emboldened by the backlash against deposed Egyptian President Mohamed Mursi, has been protesting daily.

Across the capital, around 10,000 opposition protesters rallied against the government. They vowed a mass march on Sunday and an even bigger rally on Wednesday to mark the death of politician Chokri Belaid, who was gunned down six months ago.

'COUNTER-REVOLUTION WILL NOT SUCCEED'

Ennahda party chief Rachid Ghannouchi joined the throngs of demonstrators at the pro-government rally and gave a defiant speech to wild cheers from the crowd.

"Tunisia is a candle whose revolution lit up the world but now they (the opposition) want to put it out by trying to set off a coup," Ghannouchi said.

"The counter-revolution will not succeed."

Kasbah Square was the site of major rallies in the days after Ben Ali was toppled in which demonstrators demanded a transitional Constituent Assembly to draft a new constitution.

That assembly - which the opposition is demanding be dissolved - is eight months late delivering the draft but says it is only weeks away from finishing the job.

Earlier on Saturday, Prime Minister Ali Larayedh appealed to demonstrators on both sides for calm.

"Tunisia is in need of national unity. ... I call for calm so the army and security forces can combat terrorism and not waste efforts on protests," Larayedh told a news conference.

Tunisian forces launched air and artillery strikes on Friday to try to rout militants who killed eight soldiers this week in one of the deadliest attacks on security forces in decades.

Over the past week, a roadside explosive device and a car bomb targeted security forces in Tunis, the first such attacks to hit the capital. No one was hurt.

The Interior Ministry said on Saturday that security forces foiled a plot a day earlier to assassinate a prominent politician in the coastal town of Sousse, a week after assailants killed leftist politician Mohamed Brahmi in Tunis.

The ministry said two "dangerous terrorists" were arrested for suspected involvement in the attempt. A third was still on the run after trading machine-gun fire with security forces.

'CRYING FOR MY COUNTRY'

At the opposition protests, demonstrators shouted, "After the bloodshed, the Ennahda gang has lost its legitimacy."

Ordinary Tunisians who say the economy and security situation is deteriorating and the government has not done enough have joined in daily protests this week led by the secular opposition.

The opposition insists their demands for the government's downfall are legitimate because they reflect what the people want.

But in Kasbah Square, demonstrators invigorated by the largest protest this week say they are still the majority.

"Look at the popular will, its right here now," said Adel Munir, an unemployed 28-year-old. "Yes there are a lot of problems but we had an election. This is democracy."

Planned talks on the political and security crisis on Saturday failed to produce results, as the main opposition groups declined to attend.

Instead, both sides have held their ground: Ennahda refuses to remove the prime minister and calls the Constituent Assembly a "red line." The opposition says both the assembly and the government must be dissolved.

"I'm crying for my country," said Seif Benomar, a bank employee who attended the opposition rally but said he felt disillusioned by the ongoing street protests.

"Will this of force help those who are out of work and will it stop the rise in prices? This is serving the interests of politicians and the people are just the fuel."