The UN warned Friday of soaring human rights violations in Sudan's Darfur region and said they were "verging on pure evil," amid escalating fighting seven months into the war.

"We keep saying that the situation is horrific and grim. But frankly, we are running out of words to describe the horror of what is happening in Sudan," said Clementine Nkweta-Salami, the UN humanitarian coordinator for Sudan.

"We continue to receive unrelenting and appalling reports of sexual and gender-based violence, enforced disappearance, arbitrary detentions and grave violations of human and children's rights," she told reporters.

"What is happening is verging on pure evil," she said, citing reports of young girls being raped in front of their mothers.

She said she was worried about the risk of a repeat of the genocide of the early 2000s in this region of western Sudan.

The UN refugee agency (UNHCR) pointed to reports that more than 800 people had been killed by armed groups in Ardamata in West Darfur, an area that so far had been less affected by the conflict.

"We have received these reports from new arrivals in Chad, these are refugees fleeing the Darfur area, that are talking about armed militia going from house to house killing men and boys," spokesman William Spindler told reporters in Geneva.

"These killings reportedly have happened in the last few days," he added.