Cheering residents honked horns, danced and banged on saucepans as some 200 French troops rolled into the mainly Christian town of Bouar in the west of the country.
Weary of months of violence from a rebellion that overthrew the government in March, provoking bloody sectarian clashes between Muslim and Christian communities, the residents yelled out “Thank you!” and “Save us!”
The communal violence, which has terrorised rural towns for months, flared in the capital Bangui on Thursday, leaving at least 300 dead in a wave of attacks, the Red Cross said.
Central African Republic President Michel Djotodia declared a three-day period of mourning from Sunday for the victims.
In comments on national radio he said the situation was under control and urged people to return to normal routines.
Djotodia also expressed his gratitude to France for its military help.
French President Francois Hollande, describing the bloodshed as “terrifying”, announced he would send 400 more troops than previously envisaged, boosting a UN-mandated force to 1,600 troops by Saturday night.
He said this number would not increase and most troops would not stay more than six months.
The French presidency also announced the African Union would boost the regional MISCA force to 6,000 troops from a planned 3,600.
Hollande said the job of the French and African troops would be “to disarm militias who are acting like gangsters, raping women and even killing people in hospitals”.