(Adds further Le Drian quotes and CAR PM)
PARIS, Dec 6 (Reuters) - French reinforcements arrived in the Central African Republic capital Bangui on Friday to bolster a force due to rise to 1,200 in coming days, Defence Minister Jean-Yves Le Drian said.
"The operation has effectively started," Le Drian told RFI radio of patrols by French troops, adding that one company had arrived in Bangui from a French base in nearby Gabon, and that a helicopter group was due to be in place later in the day.
He added that the night had been calm after fighting on Thursday between mainly Muslim former rebels now in charge of the country and a mix of local Christian militia and fighters loyal to ousted president Francois Bozize. A Reuters witness and an aid worker said at least 105 people were killed.
Speaking hours after securing U.N. backing for the mission on Thursday, French President Francois Hollande vowed that the French operation would be limited in time with the aim of handing over security to African forces when possible.
However doubts immediately emerged over the exact timetable. Le Drian said "it was not impossible" that France could wind down its presence after six months while Central African Republic Prime Minister Nicolas Tiangaye said it was likely they would have to remain longer.
"Six months seems a bit short to me, in my view we are looking at a year. If it (the French force) manages to sort of the problems, so much the better, but I would prefer that it stays in place for a year," Tiangaye told RTL radio.
The former French colony has slipped into chaos since mainly Muslim rebels seized power in March, leading to tit-for-tat sectarian violence with the Christian majority. However, the violence on Thursday was the worst the capital has seen during this year's crisis.
As of Thursday, France had some 650 troops based at Bangui airport - a number Hollande said would double immediately with reinforcements from French bases in neighbouring countries.
It is the second major African operation for France this year after it sent troops into Mali to halt an advance by a Qaeda-linked rebels towards the capital Bamako.
Foreign Minister Laurent Fabius said the annual Africa-France summit starting in Paris later on Friday would discuss CAR operations, including the future handover from France to African-led or U.N.-led forces. (Reporting by Mark John and John Irish; editing by Astrid Wendlandt)