France's defence minister has urged soldiers "to give themselves up" if they are guilty of sexually assaulting hungry Central African kids, as questions remain on why the probe into the alleged crimes is taking so long.

In an interview published Sunday, Jean-Yves Le Drian said he felt "disgust" and "betrayal" when he received a leaked UN report in July last year alleging soldiers dispatched to the country to restore order after a 2013 coup had sexually assaulted kids in exchange for food.

"When a French soldier is on a mission, he is France," the minister told the JDD weekly.

"If one of them has committed such acts, they must immediately give themselves in."

The abuse reportedly took place at a centre for displaced people near the airport of the Central African capital Bangui between December 2013 -- when the French operation began -- and June 2014.

UN rights investigators conducted a probe into the allegations in the spring of 2014, and a UN employee later turned the report over to French authorities because he felt his bosses had failed to take action.

Le Drian said he immediately gave the report to the courts, adding that an internal army probe into the matter was conducted and finished in August.

"It is naturally available to the courts, which are tasked with conducting the judicial probe," he said.

Asked why the investigation opened by prosecutors was still not finished nine months after the ministry received the leaked report, Le Drian said it was a "complex investigation."

"Since the alleged events, most soldiers have left that theatre of operations, but that must not stop the courts from doing their job swiftly."

According to the JDD, which saw a copy of the leaked UN report, the six children testifying against the soldiers have given very precise descriptions of tattoos and nicknames.

But a French judicial source said last week that of the 14 soldiers implicated in the probe, only a few had actually been identified.

Soldiers from Chad and Equatorial Guinea are also accused, said Paula Donovan of the AIDS-Free World advocacy group which saw the report.

"One of the children interviewed said that he had seen his friend, aged 9 or 10, with 2 soldiers from Equatorial Guinea," Donovan told AFP by e-mail.

"The friend performed fellatio and was sodomised by one soldier while the other kept watch, and then the soldiers exchanged roles."