* Tunisian unions to stage general strike on Friday
* Protests over killing of opposition leader resume
* Ruling Islamist party split over move to dismiss cabinet
* Secular opposition demands consultations
* Analysts say prolonged uncertainty could deepen upheaval (Adds analyst on escalation risk, paragraphs 12-13)
By Tarek Amara
TUNIS, Feb 7 (Reuters) - Tunisia's governing Islamists rebuffed on Thursday a plan by their party chief and prime minister to replace the government after unrest erupted over the killing of an opposition leader, deepening the worst crisis since the country's 2011 revolution.
Turmoil in the North African state that spawned the Arab Spring uprisings flared anew, with protesters setting ablaze the local headquarters of the main Islamist Ennahda party and a police station in the provincial town of Kelibia.
Police fired teargas to scatter protesters near the interior ministry in Tunis and stone-throwing youths in the southern mining town of Gafsa, where at least seven were injured. Crowds ransacked electronics shops in Sfax.
Further disturbances loomed on Friday when labour unions planned a general strike in protest at the assassination of secular politician Chokri Belaid, and his politically charged funeral expected to be held as well.
An aide to Hussein Abassi, leader of the UGTT union, Tunisia's biggest, said he had received a death threat after announcing the country's first general strike in 34 years.
Wary of further violence, many shops in Tunis closed at 2 p.m. (1300 GMT) while France, the old colonial power in Tunisia, said it would shut its schools in Tunis on Friday and Saturday.
Prime Minister Hamdi Jebali of Ennahda announced late on Wednesday he would dismiss the government led by his moderate Islamist party in favour of a non-partisan cabinet until elections could be held soon. But the idea met swift resistance.
A senior Ennahda official said Jebali had not sought approval from his party, suggesting the Islamist group was split over the move to supplant the governing coalition.
"The prime minister did not ask the opinion of his party," said Abdelhamid Jelassi, Ennahda's vice-president. "We in Ennahda believe Tunisia needs a political government now. We will continue discussions with other parties about forming a coalition government."
Ennahda's two secular coalition partners as well as the main opposition parties also rejected any move to a government of technocrats, demanding as well that they be consulted before any new cabinet is formed.
Political analysts said protracted deadlock could aggravate the unrest, which has underscored the chasm between Islamists and secular groups who fear that freedoms of expression, cultural liberty and women's rights are in jeopardy just two years after the Western-backed dictatorship crumbled.
"In the likely event that there is no agreement, civil unrest will increase, reaching a level that cannot be contained by the police," said Firas Abi Ali of the London-based Exclusive Analysis think-tank.
"If unrest continued for more than two weeks, the army would probably reluctantly step in and back a technocrat government, as well as fresh elections for a new Constituent Assembly."
Belaid was shot as he left home for work on Wednesday by a gunman who fled on the back of a motorcycle. That sent thousands of protesters into the streets nationwide hurling rocks and fighting police, similar to disturbances in Egypt last month.
No one claimed responsibility for the killing, and the head of Ennahda said the party had nothing to do with it.
But a crowd set fire to the Tunis headquarters of Ennahda, which won the most seats in a free election 16 months ago. Protests also hit Sidi Bouzid, fount of the Jasmine Revolution that ousted dictator Zine al-Abidine Ben Ali in January 2011.
While Belaid had only a modest political following, his sharp criticism of Ennahda policies spoke for many Tunisians who fear religious radicals are bent on snuffing out freedoms won in the first of the revolts that rippled through the Arab world.
PARLIAMENT TO WEIGH NEW CABINET
Pressured by Wednesday's explosion of unrest, Jebali declared that weeks of talks on reshaping the government had failed amid infighting within his coalition. One secular party threatened to bolt unless some Ennahda ministers were sacked.
Mehrzia Abidi, vice-president of the interim parliament that has been struggling for months to draft a new constitution, said it would discuss Jebali's proposal for a temporary government of experts on Thursday, but this had not happened by nightfall.
Sadok Belaid, a constitutional law expert, said the assembly would have to approve the cabinet overhaul. But the assembly's dysfunctional record raised the risk of drawn-out paralysis.
"It seems the opposition wants to secure the maximum possible political gains but the fear is that the ... crisis will deepen if things remain unclear at the political level," said political analyst Salem Labyed.
"That could increase the anger of supporters of the secular opposition, which may go back to the streets again."
Many Tunisians complain that radical Salafi Islamists could hijack their democratic revolution, fearing Ennahda is coming increasingly under their sway.
Nervous about the extent of hardline Islamist influence and the volatility of the political impasse, global powers urged Tunisians to see through a non-violent shift to democracy.
"The revolution at the beginning was a fight for dignity and freedom, but violence is taking over," said French Foreign Minister Laurent Fabius. "I want to offer France's support to those who want to end the violence. We cannot let closed-mindedness and violence take over," he said on BFM-TV.
But discontent has festered for some time, not only over secularist-Islamist issues but also over the lack of progress towards better living standards expected after Ben Ali's exit.
"We are already suffering from recession since the revolution. We rarely see tourists now, and this violence will deprive us even of our Tunisian customers," said Fethi Ben Saleh as he closed his Tunis gift shop early on Thursday afternoon.
"I do not care about this conflict between Islamists and secularists. I hate them all," the frustrated merchant said.
In a reflection of investor fears about the crisis, the cost of insuring Tunisian government bonds against default rose to their highest level in more than four years on Thursday.
Shortly before his death, Belaid said tolerance shown by Ennahda and its two, smaller secularist allies toward Salafists had allowed the spread of groups hostile to modern culture in what has been one of the most broadly secular Arab states.
As in Egypt, secular leaders have accused Islamists of trying to cement narrow religiosity in the new state. This dispute has held up a deal on a constitution setting the stage for a parliamentary election, which had been expected by June. (Additional reporting by Jeremy Gaunt in London, John Irish in Paris; Writing by Mark Heinrich; Editing by Jon Boyle)