A senior UN official has urged the world to pressure the Sudan government and rebels into ending human rights abuses in the western Darfur region.
UN emergency relief co-ordinator Jan Egeland said the organisation was getting daily reports of atrocities but was unable to help those affected.
He accused the government in Khartoum of tolerating "ethnic cleansing" by Arab militias.
"We must put pressure on the parties," he told the Security Council on Friday.
Hundreds of thousands of civilians have been displaced in the fighting, with more than 100,000 fleeing across the border into neighbouring Chad.
Fighting in Darfur broke out more than a year ago, when rebels attacked government targets, saying black Africans were being oppressed in favour of Arabs.
Mr Egeland described it as one of the world's worst humanitarian crises.
Thousands of people had been killed in the region and there were reports of mass rape by the Arab militias.
He said it appeared to be an organised campaign of ethnic cleansing, with villages looted and burnt down and food and seed supplies destroyed in a "scorched earth" policy.
The war in Sudan has created a huge refugee problem
"I've had colleagues from my office seeing in desperation people being killed, gang-raped, abused and not being able to do anything to help," he said.
He warned that there was a possibility of mass starvation and said a new UN appeal would need $115 million, with an added $30 million to care for refugees.
Aid workers can only reach a third of those affected due to government travel restrictions and insecurity.
The UN is also planning to send a fact-finding mission to Darfur in the next few days to investigate alleged human rights abuses.
On Friday a report by New York based rights group Human Rights Watch also accused the Sudanese authorities of committing crimes against humanity in the region.
The government has dismissed the claims as "a heap of lies".
On Wednesday rebels from the Sudan Liberation Movement (SLM) and the Justice Equality Movement (Jem) began indirect talks with government representatives in the Chadian capital, Ndjamena, aimed at ending the war.
But the Jem rebels say they plan to withdraw from the talks.
Fighting in the west of Sudan has intensified as government peace talks to resolve a 20-year war with rebels in the south of the country are nearing an end.
But the UN is concerned that the Darfur conflict could undermine the separate peace talks taking place in Kenya with the southern rebels.