A soldier serving in France's Sangaris force in the CAR has been accused of sexually abusing a teenage girl, who had a child in April, the UN rights commissioner Zeid Ra'ad Al Hussein revealed on Thursday.
She has lodged a paternity claim with local authorities.
France intervened in its former colony in 2013 following violence between Christian militias and largely Muslim Seleka rebels that has led to the de facto partition of the country.
"We simply have to find ways to prevent such odious acts being committed by any soldiers anywhere who are supposed to be protecting vulnerable populations," Zeid said in a statement on Thursday during a visit to the CAR.
He said French authorities have been informed of the latest accusations.
French Defence Minister Jean-Yves Le Drian has ordered an internal military inquiry, according to officials working with him.
But they said that they had yet to receive official notice from the UN and promised to call on public prosecutors to open a case as soon as they had.
Disciplinary action would be taken if the allegations are proved, defence ministry spokesperson Pierre Bayle said.
The UN's children's organisation, Unicef, is providing psychological and legal support to the girl.
Allegations that 14 French soldiers, along with soldiers from Chad and Equatorial Guinea, had been involved in sexual abuse of children aged between eight and 13 hit the headlines in April this year, leading to accusations that the UN had been slow to respond.
There were further accusations of sexual abuse involving French soldiers, this time in Burkina Faso, in July.