The top UN envoy in the Democratic Republic of Congo said two peacekeeping patrols were not informed by villagers that mass rapes were taking place near one of its bases.
Rebels from the Mai Mai militia and Rwandan Hutu FDLR, who occupied the town of Luvungi in North Kivu province from July 30th to August 3rd, raped and assaulted at least 154 civilians, according to UN figures.
According to an American aid worker and a Congolese doctor, the rebels gang-raped nearly 200 women and some baby boys.
UN special representative ti DR Congo Roger Meece said the United Nations is now working to improve communications and prevent any recurrence.
He said peacekeepers did not learn about the "horrific" rapes of for nearly two weeks, which showed that the force's actions to protect civilians were insufficient and need to be improved. He said one idea being pursued was to have villages report to the UN's forward operating base at Kibua every day.
If the force did not receive a report, he said, it would assume there was a problem and send a patrol to investigate.
The United Nations has a peacekeeping force of nearly 20,000 members in DR Congo.
Mr Meece gave the most detailed account of the UN's actions since Monday's report that Rwandan and Congolese rebels gang-raped nearly women and baby boys over four days not far from Kibua in eastern Congo's mining district. He spoke to reporters at UN headquarters by videoconference from Goma in eastern Congo.
Will F.Cragin of the International Medical Corps said on Monday that aid and UN workers knew rebels had occupied Luvungi town and surrounding villages the day after the attack began on July 30th. He said his organisation was only able to get into the town after rebels ended their brutal spree of raping and looting and withdrew of their own accord on August 4th.
The UN was not made aware of the attacks until more than a week later, despite the fact that UN patrols had been in Luvungi twice after the attacks began.
Pressed on why two UN patrols learned nothing about the mass rapes, Mr Meece said he could only speculate, noting that communication is always a problem in Congo.
"There is, of course, a significant amount of cultural baggage ... associated with rapes in this area, as well as elsewhere." he said.
"Is it conceivable that the local villagers were afraid of reprisals if they reported anything to Monusco? Possible. Is it conceivable that they were ashamed of what has happened in some form? That's possible.
"I can only speculate as to what may have been the reasons, but I know that these can be very powerful in the local society and environment," he said.
The United States will help any effort to bring to justice rebels accused in the mass rapes, Secretary of State Hillary Clinton said.
"This horrific attack is yet another example of how sexual violence undermines efforts to achieve and maintain stability in areas torn by conflict but striving for peace," Ms Clinton said in a statement yesterday.
"The United States will do everything we can to work with the UN and the DRC government to hold the perpetrators of these acts accountable, and to create a safe environment for women, girls, and all civilians living in the eastern Congo," she vowed.
The United Nations adopted a resolution last year recognising the importance of preventing and responding to sexual violence as a tactic of war against civilians.
Ms Clinton said it was now time for member nations to go beyond that with specific steps to protect civilians against sexual violence and prosecute those who commit such atrocities.
AP