This underlined the challenge the new interim president faces in restoring peace.
A French military source also said its soldiers were involved in overnight clashes after coming under attack from unidentified gunmen.
Close to one million people, or a quarter of the population, have been displaced in the former French colony by clashes that began when mostly Muslim Seleka rebels seized power in a coup in March.
Christian self-defence groups known as "anti-balaka" (anti-machete) have since taken up arms against them, and the United Nations estimates that tit-for-tat violence has claimed more than 2,000 lives.
Antoine Mbao Bogo, president of the Central African Red Cross Society, said nine of 11 bodies collected from Bangui's mostly Muslim northern neighbourhood of PK11 earlier this week had been set alight.
"They were not buried, they were dumped on the ground behind the military camp," he told Reuters by telephone.
He added that the Red Cross had collected 87 bodies in the past five days across the country.
The arrival of a 1,600-strong French military mission and another 5,000 African Union peacekeepers has so far failed to stop the fighting. This week the European Union said it would send 500 troops to support them.
Interim President Catherine Samba-Panza, the mayor of Bangui appointed as leader on Monday, has pledged to meet with armed groups in an effort to restore order.
She replaced former interim President Michel Djotodia, who is linked to Seleka and stepped down on Jan. 10 amid intense international pressure.
Elsewhere in the capital on Wednesday, residents reported light weapons fire in a northern neighbourhood, and a French military source in Paris confirmed their involvement.
"Unidentified gunmen opened fire on French forces, who fired back," said the source.
A Reuters witness said that a crowd of angry Christian residents armed with machetes and wooden weapons gathered in the neighbourhood of Ngaragba, near the French embassy, to protest against ongoing attacks by Seleka.
The protesters burned tyres as French troops tried to contain them. At least three prisoners escaped from the central jail in the confusion, the witness said.
"Last night and even this morning they came to attack us. We don't know where we will live next," said former corporal Bernard Desire Mariano, referring to Seleka attacks.
Aid workers said they could struggle to feed Bangui's displaced population, including around 100,000 sheltering at the airport, because food supplies had been disrupted due to UN truck drivers going on strike.