U.N. peacekeepers in Congo (search) sexually abused and exploited women and girls, some as young as 13, according to a report released by a U.N. watchdog agency Friday.

Peacekeepers regularly had sex with Congolese women and girls, usually in exchange for food or small sums of money, an investigation by the Office of Internal Oversight Services (search) found.

"We have had and continue to have a serious problem of sexual exploitation and abuse," said William Lacy Swing, the secretary-general's special representative to Congo, said Friday at a news conference.

"We are shocked by it, we are outraged, we are sickened by it," he said. "Peacekeepers who have been sworn to assist those in need, particularly those who have been victims of sexual violence, instead have caused grievous harm. It is inexcusable behavior, we are determined to stamp it out."

Sexual activities continued even while the investigation was going on in Bunia (search) between May and September 2004, the report said.

"It was clear that the investigation did not act as a deterrent for some of the troops, perhaps because they had not been made aware of the severe penalties for engaging in such conduct, nor had they seen any evidence of a negative impact on individual peacekeepers for such behavior," it said.

The investigators said some military officers had tried to block their work: "On several occasions, the commanders of these contingents either failed to provide the requested information or assistance or actively interfered with the investigation."

The problems were "serious and ongoing" and it was "disturbing" that there was no deterrence or protection program, the report by the U.N. oversight agency said.

The team investigated 72 allegations against both military and civilian U.N. personnel, which resulted in 20 case reports. One case involved a U.N. civilian; the others, peacekeepers.

"In six cases, the allegations against the peacekeeper were fully substantiated, and underage girls were involved in all of them," the report said, adding that none of the peacekeepers admitted to the allegations.

In other cases the evidence was either convincing, but not fully substantiated or could not be corroborated, according to the report.

The U.N. watchdog recommended that the countries that sent the peacekeepers should take appropriate action. Peacekeepers fall under the jurisdiction of the military in their own countries.

Jean-Marie Guehenno, U.N. Undersecretary-General for Peacekeeping operations said Friday that trying soldiers after they returned to their home countries was "one of the areas where we need to do better." He suggested that courts martial should take place in the countries where the crimes were committed.

Guehenno said the abuse undermined the credibility of the United Nations. "When we betray the trust they place on us it is unconscionable," he said. "It is a big stain on us. We have to go at it in great determination."

He said the sex abuse had "tainted" other U.N. staff in the country.

He declined to "name and shame" countries whose troops have committed sex abuse, saying that would lead to less cooperation from the member states in cracking down on the exploitation.

"If you do it in an adversial way you are going to have the Secretariat against the Member States and it is not going to work," he said.

He also said the investigative capability needed to be "beefed up" and rules and regulations needed to be tightened in some cases.

Under the code of conduct, soldiers are banned from engaging in sexual relations with girls under 18 years old. Asked whether he thought sex with civilians of all ages should be banned to protect desperate women from exploitation, he said the rules could be improved.

"When you are in a broken country with extreme misery and you insert a force with power, with money, the imbalance between power and money and that extreme misery, the risk of that imbalance creating an exploitative relationship is quite high. That is why we need to take extra measures and that is why I believe that the present rules are good enough in a normal environment, they are not good enough in the kind of environment that we see in post-conflict situations," he said.

Many girls in Bunia had been raped or sexually abused by local warring factions. Left without family or means of support, the presence of the peacekeepers "augmented the problem" according to the report.

In one case, a 14 year-old girl was given $1 or $2 or two eggs in return for sex. She was able to identify the soldier because he had a broken arm. She had sex with another soldier in return for $3 and a packet of milk.

Another 14 year-old girl was given $2, chocolate and bread in return for sex. A 13-year-old girl said she and her friends would go to the camp to have sex with different soldiers for between $3 and $5 for each sexual encounter.