The United Nations’ failure to respond to allegations that French peacekeepers sexually abused children in Central African Republic amounted to “gross institutional failure” and allowed assaults to continue, according to an independent panel’s damning report released on Thursday.

The study, commissioned by the UN, found that children as young as nine were encouraged to take part in oral sex in exchange for food or money in the middle of a war zone. The alleged perpetrators were mainly French soldiers from a unit known as the Sangaris force which was operating under authorisation of the security council but not under UN command.

The inquiry report, entitled Taking Action on Sexual Exploitation and Abuse by Peacekeepers, exonerated Anders Kompass, the director of field operations for the UN’s office of the high commissioner for human rights – the whistleblower who first disclosed the abuse. He had been suspended for disclosing an internal report on abuse to French prosecutors.

Initial complaints in early 2014, the report said, were “passed from desk to desk, inbox to inbox, across multiple UN offices, with no one willing to take responsibility”.

Even when the French government became aware of the allegations and sought the cooperation of UN staff, its requests were met with resistance and “became bogged down in formalities”.

UN staff, it is said, became overly concerned with whether the allegations had been improperly leaked to French authorities and focused on protocols rather than action. Among those said to have looked the other way were the UN children’s agency, Unicef, as well as human rights officials.

The UN secretary general, Ban Ki-moon, expressed “profound regret that these children were betrayed by the very people sent to protect them”. He said he accepted the panel’s broad findings.

The panel, led by the Canadian judge, Marie Deschamps, found that UN staffers failed or hesitated to pass the children’s allegations to more senior officials, sometimes because of political concerns with France.

“Not only were there unconscionable delays in providing the children with basic medical care, psychological support, shelter, food, or protection, but no steps were taken to locate the additional child victims … to determine if they also required protection and care,” the report states. There was a failure to vet peacekeepers sufficiently to screen out those with a history of past abuse.

Four French soldiers are being questioned in an investigation into alleged child sexual abuse in CAR. A total of 14 people are said to be under investigation.

Referring to Kompass, the report recognised his seniority, extensive experience with field missions and the fact that human rights officials “had not followed up on the allegations despite the need for urgent action”.

Kompass, it adds, had received “assurances that the information would be kept confidential and, more importantly, that France would take action to bring the perpetrators to justice … No adverse finding is made against the director on this issue.”

In May, an appeal tribunal had ordered the UN to immediately lift the suspension of Kompass.

So far, more than a year and a half after UN officials first heard the children’s allegations of sexual abuse, no one has been arrested, the panel points out.

The report tackles one of the most persistent and embarrassing problems for the UN and its member countries. Tens of thousands of peacekeepers serve in some of the world’s most volatile areas.

The abuse in CAR’s capital, Bangui, emerged in the middle of a chaotic war. The country had been torn apart by violence between Christians and Muslims. Thousands of frightened people had sought shelter in squalid camps at the airport.

The accusations were not made public until the Guardian’s revelations in April. The French government has not explained why the investigation was kept quiet, although the French president, François Hollande, has promised tough punishment for any soldier found guilty.

The alleged abuse took place as French peacekeeping troops were supposed to be protecting civilians at a centre for displaced people near the airport in Bangui, between December 2013 – when the French military operation began – and June 2014.

Similar accusations of abuse have emerged against soldiers from Chad and Equatorial Guinea serving in CAR.

In its conclusion the panel said: “The persistence of serious crimes against vulnerable local populations perpetrated by some of the very individuals charged with protecting them puts at risk the sustainability of peacekeeping missions in the longer term.

“The UN must take immediate action when it receives reports of sexual violence by peacekeepers to stop the violations and hold the perpetrators accountable … Above all, UN staff and agencies must end the bureaucratic cycle in which responsibility is fragmented and accountability is passed from one agency to another.”

It added: “When peacekeepers exploit the vulnerability of the people they have been sent to protect, it is a fundamental betrayal of trust.” The Guardian