A French charity worker and a churchman were abducted on Monday in Bangui, the capital of Central African Republic, the French Foreign Ministry and the Caritas charity said.

The 67-year-old woman was working for a charity providing health and education support to Central African villages, the ministry said in a statement.

The French ambassador in Bangui is in contact with the archbishop's office in the city, which has started negotiations with the captors, thought to be from the mainly Christian anti-balaka militia. They have demanded the release of one of their leaders, captured by UN forces on Saturday.

Abby Elysée Guendjiandé, national secretary of Caritas, said a pickup truck carrying three people including the French woman was stopped on the northern outskirts of the capital, which is controlled by the anti-balaka.

The charity worker and the churchman were seized, while a third person was not taken because the militia men took him for a driver, he said.

"When we called ... (her) telephone later the kidnappers picked up and said: 'Release our General Andilo and we will liberate the hostages,'" Guendjiandé told Reuters.

Andilo – real name Rodrigue Ngaibona – was detained 195 miles north of the capital, Bangui, on Saturday. He is a leader of the so-called Christian 'anti-balaka' militia formed to combat the mostly Muslim Seleka rebels who seized power in the majority Christian country in 2013. The anti-balaka brigades have been accused of atrocities including cannibalism and ethnic cleansing, leading to almost the entire Muslim population of the south of the CAR fleeing and becoming refugees.

In a report released last October UN experts said: "Andilo is currently the most enigmatic, feared and powerful military commander of the anti-balaka."

A spokesman for Caritas in Paris told Reuters the Frenchwoman does not work directly for Caritas but for the Catholic church's local health desk and two churchmen from the Holy Ghost congregation were in the vehicle.

Additional reporting by Reuters.