At least 387 men, women and children were sexually assaulted during the attacks, carried out by Rwandan FDLR rebels and a local Congolese armed group in the Walikale region of North Kivu province between July and August 2010.

Last month the UN said as many as 170 women were raped by former rebels who had deserted from the army in South Kivu in eastern Congo where increasingly fragmented armed groups are battling the Congolese army, backed by UN peacekeepers, over control of land and mineral resources.

The Walikale rapes last year caused an international outcry but only one person has been prosecuted for their role in the attack, carried out by as many as 200 armed men, the UN said.

Not enough was being done to bring the perpetrators to justice and end the impunity which is seen as encouraging further attacks, Navi Pillay, the UN's High Commissioner for Human Rights said in a statement.