UNITED NATIONS (AP) — The United Nations reported that more than 500 systematic rapes were committed by armed combatants in eastern Congo since late July — more than double the number previously reported — and accepted partial responsibility for not protecting citizens.

U .N. Assistant Secretary-General for Peacekeeping Atul Khare told the U.N. Security Council on Tuesday that at least 267 more rapes occurred in another area of the country’s east, in addition to 242 rapes earlier reported in and around Luvungi, a village of about 2,200 people located about 20 miles (30 kilometers) from a U.N. peacekeepers’ camp.

“While the primary responsibility for protection of civilians lies with the state, its national army and police force,” said Khare, “clearly, we have also failed. Our actions were not adequate, resulting in unacceptable brutalization of the population of the villages in the area. We must do better.”

The U.N. peacekeeping force in Congo, called MONUSCO, on Sept. 1 launched an operation using 750 troops to back efforts by Congolese security forces to arrest the perpetrators of the attacks, said Khare. At least 27 rebels armed with automatic rifles have surrendered and at least four more have been arrested, he said.

Meanwhile, Khare said, peacekeepers will undertake more night patrols, and perform more random checks on communities. The U.N. is also looking into ways of providing peacekeepers with mobile phones by installing a high frequency radio in Luvungi, he said.

Rape as a weapon of war has become shockingly commonplace in eastern Congo, where the government army and U.N. peacekeepers have failed to defeat the few thousands rebels responsible for a protracted conflict fueled by vast mineral reserves. Luvungi is a farming center on the main road between Goma, the eastern provincial capital, and the major mining town of Walikale.

Khare told reporters after the council session that over 15,000 rapes were reported in Congo in both 2008 and 2009.

Ambassador Susan Rice, the U.S. representative to the United Nations, called Tuesday’s briefing “very frank, comprehensive and illuminating” and said she looked forward to more sessions examining ways to prevent future mass rapes in Congo.

U.N. Secretary-General Ban Ki-moon in recent days sent Khare to Congo to investigate why U.N. peacekeepers didn’t learn about at least 242 mass rapes in the Luvungi area from July 30 to Aug. 4 until Aug. 12, when it was informed by the International Medical Corps which was treating many of the victims.

The additional sexual attacks, in an area called Uvira and other regions of North and South Kivu, came to light during Khare’s trip. He told council members he learned of 74 cases of sexual violence, including against 21 minors — all girls between the ages of 7 and 15 — and six men, in a village called Miki, in South Kivu. All the women in another village, Kiluma, may have been systematically raped, he said.

Khare said in a community called Katalukulu, 10 women were raped by Congolese soldiers, which he said must “maintain a much higher standard of discipline, good behavior and conduct, and observance of human rights.”

Altogether, he detailed new reports of mass rapes on various communities that added up to at least 267.

The assistant secretary-general called for prosecution of Rwandan rebel FDLR and Congolese Mai-Mai rebels blamed for many of the attacks and U.N. sanctions against their leaders.

Margot Wallstrom, who is responsible for U.N. efforts to combat sexual violence in conflict, expressed her alarm over the increase in reported rapes, saying they show “a broader pattern of widespread and systematic rape and pillage.” A senior member of Wallstrom’s staff accompanied Khare on his recent trip.

“It is evident that rape is increasingly selected as the weapon of choice in eastern (Congo), with numbers reaching endemic proportions,” she told the Security Council. “The sad reality is that incidents of rape have become so commonplace that they do not trigger our most urgent interventions.”

Wallstrom last month warned leaders of rebel groups that they could be prosecuted by the International Criminal Court because widespread and systemic sexual violence can constitute war crimes and crimes against humanity.

Congo’s U.N. Ambassador Ileka Atoki expressed his “deep disgust” with the mass rapes and thanked the Security Council for investigating the attacks.

“These heinous acts, that have become a weapon of war, are one more episode of the unspeakable suffering that the people of Congo have been plunged for more than a decade now,” Atoki told council members.

Atoki said his country would continue to need international help to combat the attacks, characterizing national police sources as “pathetic.” But international backing for efforts to end the protracted conflict in eastern Congo are just as important, he said.

Secretary-General Ban, who had been traveling in Europe, unexpectedly flew Tuesday to Rwanda, to discuss with officials their threat to withdraw U.N. peacekeepers from Sudan if the United Nations publishes a report accusing Rwanda’s army of possible genocide in the 1990s.

The joint U.N.-African Union peacekeeping mission in Darfur is commanded by a Rwandan, Lt. Gen. Patrick Nyamvumba, and the country has over 3,200 troops and 86 police in the nearly 22,000-strong force. U.N. officials and diplomats have said a Rwandan pullout from Darfur would be a major blow at a time of increasing violence and fresh efforts to end the seven-year conflict.