The two officers from the Republic of Congo were killed by unidentified assailants, the African Union said. Also on Friday, the country’s attorney general announced that he had opened an investigation after the discovery of a mass grave with 20 bodies in Bangui, the capital.

In the morning of December 22, French soldiers of the Sangaris force was again attacked by armed group, around 800 m east of the airport near Bangui. Soldiers taking part in Operation Sangaris reported a brief exchange of fire. During the same day, a sniper fired against a French patrol which returned fire immediately.

December 23, African Union (AU) troops early on Monday fired on demonstrators protesting against the president of the strife-torn Central African Republic, killing at least one person. Several hundred Christian demonstrators crowded at the entrance to the airport in Bangui, calling for the departure of President Michel Djotodia, who became the first Muslim leader of the majority Christian country after a coup in March that unleashed waves of violence.

Around a dozen French tanks have been sent to the airport of the Central African Republic’s capital amid intense gunfire in the neighboring areas.

Automatic gunfire rattled central Bangui and tracer fire marked the sky overnight Friday, and shots could be heard from the presidential palace and a nearby military camp.

Several hundred French soldiers were patrolling Bangui's main roads on Thursday after five Chadian soldiers were killed on Wednesday. The Catholic Archbishop of the Central African Republic and a leading Muslim cleric have issued a joint appeal for a UN force to be sent to the country.

French troops were deployed on Bangui's main roads and in several districts of the capital on Thursday after gunfire and clashes on Wednesday. The French have reoriented their efforts towards the most troubled districts, such and Gobongo and Bacongo, officials said.

The violence eased on Thursday as French soldiers took up positions on main roads near the airport and in troubled neighbourhoods, although sporadic shooting was reported in several areas during the morning.

France deployed a 1,600-strong peacekeeping mission in its former colony in early December to join the 4,000-strong African Union peacekeeping mission.

France's force, codenamed Sangaris, has between 1,000 and 1,200 men stationed in Bangui, with the rest deployed in the interior of the country, said Colonel Gilles Jaron, spokesman for the French military.