(CNN) -- U.N. officials on Tuesday put the number of rapes and other sexual attacks in eastern Congo since late July at more than 500, more than double the previous estimate.

In remarks prepared for delivery to the Security Council after returning from a fact-finding trip to the region, U.N. Assistant Secretary-General for Peacekeeping Atul Khare cited 267 rapes or other sexual attacks in the town of Uvira -- on the eastern edge of the country -- and other nearby regions of North and South Kivu, in addition to the 242 rapes that had already been reported in and near the village of Luvungi.

Among the additional cases was a report of 10 women raped by members of the Armed Forces of the Democratic Republic of Congo on August 17 and 18 in the community of Katalukulu, in Fizi territory, South Kivu, he said.

On August 17, at least 40 rapes were committed in the village of Mubi by an alleged coalition of Democratic Forces for the Liberation of Rwanda and Mayi-Mayi, a militia group active in the region, he said.

Another 13 rapes occurred in Pinga area in Chuho market, he said.

On August 26, Khare received reports of 74 cases of sexual violence -- including 21 directed at girls 7 to 15 years of age -- and six men in the village of Miki in the territory of Mwenga, he said.

The incidents occurred in July and August, he said.

Five days later, he said, 130 cases of rape were recorded in several villages in the territory of Shabunda. There were reports that in one village, "all women might have been systematically raped," he said.

Khare had gone to Congo to find out why peacekeepers said they hadn't learned about the rapes near Luvungi sooner.

The United Nations reported last week that some 242 people were raped by armed Congolese and Rwandan rebels in villages in North Kivu province between July 30 and August 3.

Attackers blocked roads and prevented villagers from reaching outside communications. Many homes were also looted and burned. Many of the victims were gang-raped by as many as six men at a time, according to the United Nations Organization Stabilization Mission in the Democratic Republic of the Congo.

The rapes were first publicly reported on August 22.

The United Nations initially said it did not learn about the attacks until August 12, when it was alerted by International Medical Corps. That group said it first told the United Nations about the rapes on August 6.

But on Tuesday, the United Nations acknowledged that it first learned of a report of rape on July 30, nearly two weeks earlier than it had previously said.

"We can confirm that the Daily Field Security Report from North Kivu on 30 July included the following: 'Today 30 July 2010 during morning hours, the locality of Mpofi (52 Km E of Walikale) passed under control of FDLR [Democratic Forces for the Liberation of Rwanda] combatants. One woman was reportedly raped and locals fled towards Walikale and Kibua. More information to be ascertained.'

"We can also confirm that, on the basis of this information, an e-mail was sent by the Office for the Coordination of Humanitarian Affairs transmitting information of the FDLR movement," it said.

The July 30 internal U.N. email was relayed to relief agencies working in the area and warned that the rebels had taken over the villages, and had already committed one instance of rape.

U.N. officials have said they will toughen efforts to stop rapes in the region.

"The women of eastern DRC deserve better," said Margot Wallstrom, a U.N. special representative for sexual violence in conflict who sent a senior member of her staff with Khare on his fact-finding mission to the region. "For them, there is no safe place. They are raped when harvesting crops; when going to market; when fetching water and firewood; when carrying their babies; when in their homes at night, among their loved ones."

She added that the rape is becoming a weapon of choice in eastern DRC. "The sad reality is that incidents of rape have become so commonplace that they do not trigger our most urgent interventions," she said.

Noting that the information about the rapes "was slow to surface," she called for the United Nations to focus on how to improve its response to such reports. "We should examine the U.N.'s response, including that of our peacekeepers on the ground, not in a spirit of self-recrimination but with a determination and resolve to do better to protect civilians in what is undoubtedly one of the most complex, vast and volatile conflict zones in the world."

She noted that some rebel leaders have been identified as having been present during the attacks and called for them to be used "as a starting point" to bring the attackers to justice. "Our policies of 'zero tolerance' cannot be backed by a reality of 'zero consequences,'" she said.