Former members of the Seleka rebel group have shot dead a Central African Republic judge and his assistant, a para-military police official has said.

"Magistrate Modeste Martineau Bria ...and his aide-de-camp were cold-bloodedly killed on Saturday night" in central Bangui, the official told AFP news agency on Sunday on condition of anonymity.

"Ex-Seleka members... sped up to them on a motorbike and opened fire," he added.

The motive for the killing is not yet known. 

The landlocked nation has been mired in chaos since Seleka rebels ousted longtime president Francois Bozize in March. Seleka leader Michel Djotodia named himself president but agreed to hold elections next year.

CAR awaits UN decision on peacekeepers

He officially dissolved the rebel movement but its members have continued to stage attacks and robberies. Armed gangs, mainly former Seleka loyalists, now dominate outside the capital Bangui.

The country has seen an increase in clashes between former rebels, who are Muslim, and local self-defence groups formed by rural residents who are Christian, in common with around 80 percent of the population.

African nations have deployed some 2,500 troops in the country in a force that is due to increase to 4,500, but diplomats and many officials say it cannot cope with the anarchy and that UN peacekeepers may be needed.

UNICEF has launched an appeal for $32m to fund aid in the Central African Republic, but has so far mustered only $12m.

Source: AFP