The conflict in Sudan's western Darfur region "is now the world's greatest humanitarian and human rights catastrophe", a top UN official said in Nairobi on Friday.
Mukesh Kapila, the United Nations Humanitarian Co-ordinator for Sudan, also told journalists that the Darfur conflict, which erupted in February 2003, was "possibly the world's hottest war".
The conflict has intensified just as the Khartoum government and the country's main rebel group, the Sudan People's Liberation Army, are finalising a deal to end Sudan's wider civil war, which began in 1983.
There is considerable international pressure for these talks, held in Kenya, to reach a speedy conclusion.
Meanwhile, the Darfur war, which has only recently begun to receive serious international attention, has killed over 10,000 people and affected more that a million others, according to Kapila.
Systematic rape, a "scorched earth policy" and other attacks on civilians, he said, were "tantamount to war crimes." Kapila said such attacks had taken place on "a scale comparable to historical situations, including Rwanda" in 1994 where a genocide claimed up to a million lives.
"The only difference between Rwanda and Darfur is the numbers involved of dead, tortured and raped," he said.
"Some people are using the term ethnic cleansing. I say that was not far off the mark," he said.
In one incident in the village of Tawila two weeks ago, "at least 100 women were raped in a few hours," said the UN official.
Kapila said most of the atrocities were being carried out by militia groups fighting the rebel movement that rose up against the Khartoum government in February last year. The rebels accuse Khartoum of marginalising their region.
While declining to accuse the Sudanese government of directly co-ordinating the activities of the militia, Kapila said Khartoum "could do more to bring the Janjawid (Arab militia) under control."
"We are not seeing any progress," in that regard, he said.
The UN official said he had had reports of "planes and helicopters used in attacks on civilians in the last six weeks."