French authorities have identified some of their troops accused of sexually abusing children in Central African Republic while there on peacekeeping duties, a French judicial source said.

The matter, which risks damaging the reputation of France's military operations in Africa, came to light this week when the Guardian newspaper published an internal UN report that raised allegations of the rape of boys by French troops.

The source said an initial reading of that report suggested 14 soldiers were involved in the alleged abuse, which reportedly took place between December 2013 and June 2014.

Subsequent French inquiries had identified some of them, the source said, adding that no soldiers had been questioned yet.

President Francois Hollande, who has been a strong advocate of using the French military to help secure peace in former colonies such as Central African Republic or Mali, said anyone found guilty would be made an example of.

"If this information is confirmed ... the punishment will be proportionate to the deeds. If they are serious, the punishment will be harsh," he told reporters during a public engagement in western France.

The judicial source said soldiers of other nationalities were also implicated by the UN report, but gave no further details.

French prosecutors will also ask for an internal French army report on the matter to be declassified.

France intervened in Central African Republic, a former French colony, 18 months ago to stem violence between Christian militias and largely Muslim Seleka rebels who had seized power.

It started withdrawing some of its 2,000 troops this year, handing over to UN peacekeepers.

France's Defence Ministry confirmed the alleged abuse took place at a centre for displaced people at M'Poko airport in the capital Bangui.

It said it would take "all necessary measures" to establish the truth.