The UN has said everything possible must be done to prevent atrocities like the recent rape of more than 150 women and children in the DR Congo.
In an emergency session of the Security Council, Secretary General Ban Ki-moon said Congolese authorities had to fully investigate what had happened.
The Council also said peacekeepers in the area should have done more to protect local people from rebels.
The peacekeepers say they were not told about the attacks until 10 days later.
The rapes happened after rebels occupied Luvungi town and surrounding villages, within miles of a UN peacekeeping base.
Some reports say nearly 200 women and some baby boys were attacked by the rebels over a four-day period, before they left. The UN has confirmed 154 cases.
The Security Council said it was "of utmost importance that the Democratic Republic of the Congo continue to pursue its efforts to fight impunity".
Mr Ban, who has despatched an envoy to DR Congo, urged the authorities to "investigate this incident and bring the perpetrators to justice".
He called on officials to renew their efforts to bring peace and stability to the conflict-ridden eastern Congo and urged armed groups to give up their weapons.
But Mr Ban also said the UN had to do more to "protect civilians from such wanton violations of international human rights and humanitarian law".
He said the UN mission in DR Congo (Monusco) "does what it can within its mandate, working with limited resources in an exceptionally difficult environment".
"But, at such times, we should always ask if we could have done more," he added.
UN peacekeepers in the area say they were given no information about rebel attacks until 10 days after the incident. They say local people may have been afraid of rebel reprisal or ashamed by the rapes.
Roger Meese, the top UN envoy in the country, said he had not been at the base but knew that troops would have intervened had they known.
"Our first priority is very clearly the protection of civilians so if you have an accurate or a credible report of mass rapes going on, certainly the commander in place and the Monusco forces would have tried to take action to stop whatever was going on, but we didn't have that information," he told reporters.
The president of the Security Council, Vitaly Churkin, said the UN would conduct its own investigation into what had gone wrong.
"There was general feeling that things did not work the way they should have worked, and it is the intention of the Council to look into it very thoroughly," he said.
"Everything is to be done in order to prevent such occurrences in the future."
The attacks have been blamed on rebels from the Democratic Forces for the Liberation of Rwanda (FDLR).
But in a statement from Paris, the group's executive secretary Callixte Mbarushimana said it was "in no way involved in these odious actions and takes umbrage at the baseless accusations launched against them by the secretary general of the United Nations", the AFP news agency reported.
Eastern DR Congo is still plagued by army and militia violence despite the end of the country's five-year war in 2003.
UN peacekeeping troops have been backing efforts to defeat the FDLR, whose leaders are linked to the 1994 genocide in Rwanda and who are operating in eastern DR Congo.