UN humanitarian chief Jan Egeland has called sexual abuse in the Democratic Republic of Congo a cancer that seems to be out of control
Delivering a report to the UN Security Council, he called on the Congolese authorities to act more firmly to end violence against civilians.
Mr Egeland was speaking after visits DR Congo and Uganda last week.
He said the situation in northern Uganda was now more promising than it had been in years.
However, Mr Egeland said the challenges facing DR Congo were enormous.
He said the country - still emerging from civil war - had seen the worst haemorrhage of human life in this generation.
Four million people had been killed by war and preventable diseases in the past eight years - the equivalent of six Rwandan genocides, Mr Egeland said.
The UN and the transitional Congolese government had made much progress, but not enough to end impunity, he said.
He described being deeply shocked by the stories of women who had been abused by members of the army and militia groups.
"One woman told me she had been raped repeatedly for more than a week, by a group of soldiers who kept her bound so tightly that she had permanently lost the use of her hands," he said.
Mr Egeland said mutilations often followed the rapes.
"Military and civilian authorities are still virtually unaccountable for crimes against civilians," he warned, adding that more forceful pressure needed to be put on the army in particular.
On Uganda, Mr Egeland highlighted impunity as a key issue in the aftermath of the recent agreement between the government and rebels of the Lord's Resistance Army (LRA), says the BBC's Mike Wooldridge at the UN.
The 19-year conflict in the north became notorious for the brutality shown to children and the emptying of the countryside, our correspondent says.
Mr Egeland said people in the region were worried that indictments by the International Criminal Court against leaders of the LRA could threaten the peace process.
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