French troops shot two unidentified men at Bangui airport on Thursday morning after the men opened fire on their positions from a pick-up truck, the French military command said Friday.
Bout 2,000 people have taken refuge at the airport, according to spokesperson Colonel Gilles Jarron.
"The operation has begun insofar as the French forces that were already present at Bangui airport with a mandate limited to protect that airport and our nationals last night started patrols in Bangui," Le Drian told RFI on Friday morning.
The CAR capital was calm on Thursday night, he said, adding that a company had arrived from Gabon and that a detachment of helicopters would arrive on Friday.
The French force is currently 650 strong and will be "doubled by the end of the week", Foreign Affairs Minister Laurent Fabius told France Info radio.
The intervention's aims are to establish "minimum security, allowing a humanitarian intervention to start", which will mean "making the streets safe, some principal itineraries that allow people to at least get to hospital", and allow "the African force to be in a position to assure the security of the country ahead of a political transition".
French President François Hollande on Thursday announced an "immediate" military intervention in the CAR, where hundreds of people have been killed as violence by rebel Seleka militias and anti-balaka armed groups takes on a Christian-Muslim sectarian aspect.
"We are on the brink of mass atrocities," French UN representative Gérard Araud told CNN.
Despite the fact that France is the CAR's former colonial ruler, "nobody can accuse us of having any economic interest", he said. "It is a humanitarian intervention."
Both Hollande and Le Drian insisted that the intevention will be short, between four and six months.
Its name has been chosen to stress that intention - it is called "Sangaris" after a small red African butterfly that has a 20-day life span.
The Misca African force will have 4,000 troops and has a 12-month mandate from the UN to "protect civilians, reestablish order and security and stabilise the country".