By Erika Solomon and Tarek Amara
TUNIS (Reuters) - The red Tunisian flags they wave are the same, but the divide between opposition and pro-government protesters in the capital's main square is much wider than the 150-metre gap between barriers put there to separate them.
Nearly two years after Tunisians came together to remove the long-standing autocratic president, the country is facing its worst political crisis since that uprising set off a wave of protests across the region.
"They are traitors, they are mercenaries!" is a refrain heard on either side of Bardo Square, where thousands of people have gathered at dusk over the past few days.
And as the number of people at the square steadily grows, the stance of both the secular opposition and supporters of the Islamist-led government has hardened.
The opposition, angered by a second assassination of one of its leaders and emboldened by Egypt's army-backed ousting of the Islamist president, says it will accept nothing less than the downfall of the new transitional leadership.
Supporters of ruling Ennahda, a moderate Islamist party, accuse the opposition of trying to destroy the state out of animosity toward democratically-elected Islamists.
In addition to unrest on the streets, at stake is Tunisia's fragile democratic transition process, managed by the temporary Constituent Assembly. It says it is only weeks away from completing the draft constitution.
On both sides of an increasingly polarized confrontation, Tunisians feel they are fighting for their political survival, an anxiety that has made reactions particularly fierce.
"We need to dissolve this assembly and its constitution because they're not a government, they're terrorists," shouted secular protester Raja Haddad, wrapped in a Tunisian flag.
"Their time is up and people are fed up. We're ready for any scenario, whether it is protests or war."
CHEEK BY JOWL
Unlike in Egypt, where supporters of the ousted leader are concentrated in one area of Cairo while his opponents are in another, the rival factions in Tunis could barely be closer.
Since demonstrations began on Friday, they have swelled from a few hundred to several thousand, even up to 20,000 on the side of opposition protesters on Tuesday.
So far they have remained generally peaceful, with the exception of few stones thrown between the sides and the intervention of police firing tear gas earlier this week.
But anger has been boiling just beneath the surface since last Thursday, when opposition figure Mohamed Brahmi was gunned down, just six months after fellow politician Chokri Belaid was shot dead. The government blames hardline Salafist militants.
The opposition says that whoever was behind the attacks, they were Ennahda's fault. It feels the party has created a sense of impunity among hardline Islamists.
Monica Marks, a Tunisia-based analyst, said leaders could help ease tensions with softer rhetoric - particularly the opposition. "Instead they are going for the jugular."
Brahmi's family refused to allow Ennahda to send representatives to attend his funeral.
"Just as we buried Brahmi, we now need to bury the Ennahda government," said his fellow Popular Front leader, Ahmed Saddik, at the funeral, attended by thousands of Tunisians.
There have been previous bursts of violence since Tunisians ousted Zine al-Abidine Ben Ali.
But the aftermath has generally been seen as one of the few promising stories of an Arab uprising blighted by Syria's civil war and the Egyptian military's removal of an elected Muslim Brotherhood president - a step that triggered violent unrest.
ENNAHDA OFFERS CONCESSIONS
Ennahda has offered some concessions - it says it is open to forming a new government. But it has drawn a line at the Constituent Assembly. For the opposition, that is not enough.
"This isn't intransigence, it's disgust. Why accept more concessions when the last ones didn't stop the assassinations?" asks Mohammed Belati, an unemployed 26-year old at the protests.
Nearby, Ennahda supporters are equally angry.
"Respecting legitimacy is a duty," they shout across the square.
Historical precedent appears to be at the root of much of the animosity.
Secularists remember a string of Salafist attacks on movie theatres and liquor stores and blame it on Ennahda.
Islamists were persecuted under Ben Ali, and with many leftists suspected of old ties to his regime, they are watching Egypt's crackdown on Islamists with alarm.
"I was a political prisoner under Ben Ali. I was tortured. I refuse to go back to living under oppression and humiliation," said Monia al-Hajj, a 44-year-old woman in a white head scarf.
"If they want change, let them go to the ballot box. We keep offering concessions but they're just against our presence at all. We don't want blood, but we're ready to die for justice."
"DEMOCRACY NOT ABOUT ELECTIONS"
Tunisians are struggling to answer a question many of the region's fledgling democracies face: How do transitional states respect elections and respond to populations impatient for progress and fearful of falling back into repression?
Secular protesters like Belati say the answer is clear: "Democracy isn't actually about elections, its about popular will. The will of the Tunisian people has changed. Our movement isn't risking a crisis. The crisis is already here."
But Marks argues Tunisians should be wary of destabilizing their new government when it is so close to a new constitution and fresh elections tentatively scheduled for December 17.
"Tunisians don't have a list of horrible state violations - there's not enough reason to obliterate the transitional institutions. It's cutting your nose to spite your face."
Assembly members poured over dozens of national charters and met with experts for months to prepare their constitution. Despite opposition criticisms, international observers say they have no major objections and see no signs of Islamic radicalism.
Some Tunisians may simply be shocked by how messy democracy can be and how long reaching a consensus can take. They were promised a new constitution within a year. The Assembly is eight months late.
"They are new to it, they had never seen how democracy works up close," Marks said. "Watching the process was disturbing for them, and tiring for politicians practicing it too."
Since the revolt, Tunisians have earned a reputation for pulling back from the brink of turmoil. They may yet do it again. Even as protesters chant angry slogans, demonstrators from both sides walk past the other's camp, unafraid of attack.
On the opposition side, some religious men with long beards and women wrapped in conservative heads carves chant with them. In the Ennahda camp, some secular women drape flags over their bare shoulders.
"Oh yes, we're facing a crisis," laughed Hajar, a 27-year-old student watching the Ennahda protest from the barrier.
"I don't love these people, and I want to crush their government. But we're all Tunisians. We'll come together again."
(Reporting by Erika Solomon, Editing by William Maclean and Mike Collett-White)