By Tarek Amara

TUNIS (Reuters) - Tunisia's governing Islamists rejected on Thursday a plan by the 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.

Protests resumed in the North African state that gave birth to the Arab Spring uprisings, with police firing teargas to scatter demonstrators near the interior ministry in Tunis and stone-throwing youths in the southern town of Gafsa. At least seven people were wounded in Gafsa, witnesses said.

Labour union leaders declared a general strike for Friday in protest at the assassination of secular politician Chokri Belaid and his family said the funeral could be held then too, raising the specter of further turmoil.

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. (8 a.m. ET) 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 favor of a non-partisan cabinet until elections could be held, as soon as possible.

But 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."

Tunisia's main opposition parties also rebuffed any step towards a government of technocrats, demanding too 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.

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

Mehrzia Abidi, vice-president of the interim parliament which has been struggling for months to draft a new post-Ben Ali constitution, said it would discuss Jebali's proposal for a temporary government of experts on Thursday.

Sadok Belaid, a constitutional law expert, said the assembly would have to approve the cabinet overhaul. But the assembly's dysfunctional record raised the threat of drawn-out instability.

Political analyst Salem Labyed said the opposition appeared to want to leverage the crisis to its own advantage.

"It seems that 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. That could increase the anger of supporters of the secular opposition, which may go back to the streets again," he said.

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 smoldered 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," he 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.

Jebali declared after Wednesday's protests that weeks of talks on reshaping the government had failed amid infighting within the three-party coalition. One secular party threatened to bolt unless Ennahda replaced some of its ministers.

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)