Widespread allegations of sexual exploitation and abuse of Congolese women, boys and girls have been made against U.N. personnel who were sent to help and protect them — despite a so-called zero tolerance policy touted by the United Nations toward such behavior.

The range of sexual abuse includes reported rapes of young Congolese girls by U.N. troops; an Internet pedophile ring run from Congo by Didier Bourguet, a senior U.N. official from France; a colonel from South Africa accused of molesting his teenage male translators; and estimates of hundreds of underage girls having babies fathered by U.N. soldiers who have been able to simply leave their children and their crimes behind.

William Swing, a former U.S. ambassador to Congo who now heads the U.N. peacekeeping mission there, admitted the sexual crimes were a black mark on the United Nations.

"It pains us all," he said. "It's absolutely odious. And we're determined to wipe it out."

But Swing said the problem was just recently brought to his attention, and that only a small percentage of the 11,000 U.N. personnel in Congo were involved.

"A few people have managed to basically cause disgrace for the mission and for the U.N., and that's why we're determined to conquer it. I have sent a dozen home," Swing said. But human rights investigators have reported a far wider, even systemic problem, recording more than 150 allegations against U.N. employees in Congo.

Secretary-General Kofi Annan sent a letter to the Security Council on Wednesday announcing a set of strict measures designed to stem the sexual abuse that has haunted peacekeeping operations for decades. The Democratic Republic of Congo has the U.N.'s largest peacekeeping mission, with 13,950 soldiers and 1,875 civilian employees, and thus has the greatest potential for problems.

Peacekeepers are no longer allowed to have contact with Congolese except to carry out their official duties, and cannot even buy fruit from vendors; they must wear their uniform even when off-duty or off their base. A general curfew has been imposed from 6 p.m. to 6 a.m., and bars and some cafes have been designated off limits to U.N. soldiers and civilians. Offenders will be repatriated.

"We cannot tolerate even one instance of a United Nations peacekeeper victimizing the most vulnerable among us," Annan's letter said, adding that the sexual abuse did "great harm" to the tradition and honor of U.N. peacekeeping and the reputations of the countries that supply troops. "Most important, however, such behavior violates the fundamental 'duty of care' that United Nations peacekeepers owe to the very peoples they are sent to protect and serve."