* At least 105 people killed in fresh fighting in Bangui
* Security Council imposes one year arms embargo on CAR
* U.N. officials have warned CAR could spiral into genocide (Adds quotes from French, U.S. ambassadors, details throughout)
By Michelle Nichols and Louis Charbonneau
UNITED NATIONS, Dec 5 (Reuters) - The U.N. Security Council authorized French and African troops in Central African Republic on Thursday to use force to protect civilians, imposed an arms embargo on the country and asked the United Nations to prepare for a possible peacekeeping mission.
In a unanimously adopted resolution the 15-member council also asked U.N. Secretary-General Ban Ki-moon to establish an inquiry into human rights abuses in the landlocked, mineral-rich nation of 4.6 million people, which slipped into chaos after Seleka rebels ousted President Francois Bozize in March.
Rival militia forces clashed in Central African Republic's capital, Bangui, on Thursday. A Reuters witness and an aid worker said at least 105 people had been killed.
Mindful of the 1994 genocide in Rwanda, when hundreds of thousands were killed as the world looked on, Western powers have urged swift action to keep the anarchy in Central African Republic from leading to major atrocities against civilians.
"History has told us that the worst may happen, history has told us that the Security Council needs to act," French U.N. Ambassador Gerard Araud told reporters after the vote. "This country is in the midst of a tragic crisis."
"Thugs are killing, looting and raping on a daily basis. The Central African state has collapsed and is not able anymore to ensure the protection of its own people," said Araud, who is president of the U.N. Security Council for December.
Central African Republic's interim President Michel Djotodia, the former Seleka rebel leader, has failed to control his mostly Muslim fighters, who have preyed upon the majority Christian population, unleashing tit-for-tat killings. Rights groups say both sides may have committed war crimes.
Senior U.N. officials have warned that Central African Republic is at risk of spiraling into genocide. The United Nations estimates that 400,000 people have been displaced and 68,000 have fled to neighboring countries due to the violence.
'YESTERDAY TOO LATE'
The U.N. resolution expressed "particular concern at the new dynamic of violence and retaliation and the risk of it degenerating into a country-wide religious and ethnic divide, with the potential to spiral into an uncontrollable situation."
U.S. Ambassador to the United Nations Samantha Power described the French and African mission as the best option at the moment "to halt the carnage in the CAR the most quickly."
"Yesterday is too late," Power said. "There have been atrocities committed already. I suspect that when the (African) troops and the French troops move out of Bangui we will learn more about some of the disturbing events that have unfolded."
"We have heard accounts of tens of thousands of Christians sheltering in a church outside Bossangoa with thousands of their Muslim neighbors huddled similarly in a nearby mosque, all of them fearing the possibility of an attack," she said.
There is a 2,500-strong peacekeeping force in Central African Republic deployed by the Economic Community of Central African States. The African Union is due to take charge of that force later this month and boost its size to 3,600 troops.
The U.N. Security Council resolution authorized the deployment of the African Union force for one year, with the operation to be reviewed after six months. It also asks Ban to set up a trust fund for voluntary contributions to finance the African force, to be known as MISCA.
The European Union has offered financial support to MISCA through its African Peace Facility, while the United States has pledged $40 million to the African Union-led mission.
CYCLES OF CRISES
France, which already has around 400 troops based at the airport in the capital Bangui, is preparing to boost its force in its former colony to at least 1,000 soldiers. The council authorized "the French forces in the CAR, within the limits of their capacities and areas of deployment, and for a temporary period, to take all necessary measures to support MISCA."
The council asked Ban to "undertake expeditiously contingency preparations and planning for the possible transformation into a United Nations peacekeeping operations, stressing that a future decision of this council would be required to establish such a mission."
Ban is due to report to the council within three months on recommendations for a possible U.N. peacekeeeping mission. He said in a report last month he had already ordered officials to start preparing for such a mission and that at least 6,000 U.N. peacekeepers and 1,700 police would be needed.
Central African Republic is rich in gold, diamonds and uranium, but decades of instability and the spillover from conflicts in its larger neighbors have left the country mired in cycles of crises.
The Security Council created its first sanctions regime in 18 months by imposing an arms embargo on Central African Republic that requires all countries to prevent the direct or indirect supply, sale or transfer of arms and related materiel.
It also expressed "its strong intent to swiftly consider imposing targeted measures, including travel bans and assets freezes, against individuals who act to undermine the peace stability and security ... in the CAR."
The Security Council also demanded the swift implementation of transitional arrangements, which require free, fair and transparent presidential and legislative elections to be held within 18 months.
(Reporting by Michelle Nichols; Editing by Louis Charbonneau and Vicki Allen)