SANAA/OSLO (Reuters) - Fighting overshadowed the first meeting on Saturday of Yemen's new unity government, which is trying to avert civil war after a deal brokered by the country's Gulf neighbors for President Ali Abdullah Saleh to step down.

A Yemeni activist, accepting theNobel Peace Prize in Oslo, said the conscience of the world should be haunted by its failure to help Yemen's democratic uprising, and warned that Saleh would choose war rather than fulfill his pledge to quit.

Clashes in the southern province of Abyan killed 11 militants and two soldiers, and in the capitalSanaa a soldier was killed in overnight fighting between supporters and opponents of Saleh, officials said.

State news agency Saba said Vice President Abd-Rabbu Mansour Hadi, to whom Saleh transferred power under the deal to ease him from office, chaired the meeting of the newly sworn-in cabinet, which includes members of the opposition.

The government faces a host of challenges including sporadic fighting with anti-Saleh tribesmen, a southern separatist movement, a Shi'ite Muslim rebellion in the north and the threat from a regional wing ofal Qaeda that has exploited upheaval to strengthen its foothold in the poor Arabian Peninsula country.

If Saleh fulfills his pledge to leave, he will be the next Arab leader swept from power by the wave of protests across the Middle East andNorth Africa that has already brought down authoritarian rulers of Tunisia, Egypt and Libya this year. Syria's Bashar al-Assad is also battling an uprising.

Tawakul Karman, a 32-year-old Yemeni journalist who shared the Nobel Peace Prize with two Liberians, said that despite the president's promise, Saleh "will not leave."

"He wants to (push) the country into civil war," she told Reuters in an interview after accepting her share of the $1.5 million annual award, previously won by historic figures likeMartin Luther King and Nelson Mandela.

Her award was the Nobel Prize committee's response to what its head, Thorbjoern Jagland, called "the wind that is now blowing in the Arab world." "No dictator can in the long run find shelter from this wind of history," Jagland said.

HAUNT THE CONSCIENCE

During her acceptance speech, Karman rebuked the international community for failing to halt violent crackdowns, both in her homeland and in Syria.

"This should haunt the world's conscience, because it challenges the very idea of fairness and justice," she said. "The democratic world, which has told us a lot about the virtues of democracy and good governance, should not be indifferent to what is happening in Yemen and Syria."

In an apparent criticism of the power sharing deal, which would grant Saleh immunity from prosecution if he stands down, Karman said: "These (Arab leaders) should be brought to justice before the International Criminal Court; there should be no immunity for killers who rob the food of the people."

Leading the meeting of the new cabinet, the vice president called on ministers to help restore stability after 10 months of protests against Saleh's 33-year rule.

"Everyone in Yemen expects you to focus on the main tasks of this government and steer clear of issues which give rise to discord," Saba quoted Hadi as telling the new cabinet. Hadi also headed the first meeting of a committee of officials and senior officers overseeing the military under the transition plan.

Under the agreement, Saleh's General People's Congress and opposition parties have divided up cabinet posts with the aim of steering Yemen towards a presidential election in February.

In clashes between government troops and al Qaeda-linked militants, 11 Islamists and two soldiers were killed on Saturday east of the city of Zinjibar, a military official told Reuters. On Friday, a soldier was killed in fighting between government forces and opponents of Saleh in Sanaa, the Defense Ministry said.

The violence near government buildings and the compound of Sadeq al-Ahmar, a foe of Saleh who commands significant forces, was the latest challenge to the transition plan.

The Defense Ministry on its website accused Ahmar tribesmen of attacking the northern neighborhood of Hasaba with the aim of "derailing efforts towards establishing security and stability in the capital and other areas."

The opposition said troops from the Republican Guard, headed by a son of Saleh, broke a truce and fired artillery at northern parts of the capital on Saturday, wounding at least one person.

Saleh's troops and opposition gunmen have begun withdrawing from the streets of the city of Taiz, where days of battles that killed dozens of people had threatened to wreck the power transition deal. A committee set up to restore normality to Taiz cleared roadblocks set up by both sides and oversaw their withdrawal from occupied buildings, an official said.

(Additional reporting by Mohammed Mukhashaf in Aden and Balazs Koranyi in Oslo; Writing by Peter Graff, Editing byRosalind Russell)