The sky blue insignia and helmets are meant to stand for something, as is the organisation they represent. The sexual abuse of children by UN peacekeepers and humanitarian workers, a leading aid agency reports, is widespread and has been systematically covered up.

Some of the perpetrators have been UN peacekeepers on duty in Liberia, Haiti and Democratic Republic of Congo but it is not limited to these countries. Abuses included rape, child prostitution, pornography, sexual assault and the trading of food and mobile phones for sex.

Children told researchers that most victims were too afraid to report the crime, fearing punishment, stigmatisation or the withdrawal of aid. The crimes against children are specially reprehensible. They are the most vulnerable members of society and the fact that they have been betrayed by those sent to protect them is doubly disturbing.

The UN has said the it would investigate. That is not enough. The report said that while the UN in particular had made efforts to combat sexual abuse of children by its staff and peacekeepers in recent years, there remained "endemic failures in the response to allegations of abuse when they had been officially reported".

There are more than 200,000 of its personnel serving around the world. Of course only a tiny minority are guilty, but even if one man is guilty that is one too many. More than condemnation is needed.

The UN must instigate a comprehensive inquiry examining the evidence and bringing those responsible to immediate justice. Anything less is a betrayal of its mandate and makes a mockery of the sacrifices members of the UN have made to bring peace to war-torn areas, often paying the ultimate price.

It is hard to imagine a more grotesque abuse of authority than the flagrant violation of children's rights. Those guilty must be punished now, for all our sakes.