About 10 people were killed in infighting between "self-defence" groups in the Muslim district PK5 on Sunday evening, according to local sources.
Earlier reports put the death toll at four.
Residents continued to flee the area on Monday morning.
France's Operation Sangaris started three years ago, aiming to end sectarian bloodletting between armed Christian and Muslim gangs following the toppling of president françois Bozizé.
Some 350 French troops will remain as security is left in the hands of the UN's Minusca force.
"France will keep its commitment to the CAR," Valls told RFI while on a visit to Côte d'Ivoire Sunday. "There is no question of leaving this country alone."
Government alleges plot
French Defence Minister Jean-Yves Le Drian was to meet President Faustin-Archange Touadéra and address the CAR parliament on Monday.
Violence in the centre of the country cost 25 lives two days before his trip.
"Machiavellian plan hatched by the enemies of peace" is targeting people in Bossangoa, Bozoum and Bocaranga in the north of the country, a government statement claimed.
"We are very worried about the serious incidents in the last few days," Valls said in his RFI interview.