Actor George Clooney has spoken of the horrors he witnessed when he visited the Sudanese region of Darfur, saying the area urgently needs peacekeepers.
Mr Clooney recently returned from a trip to Darfur
The Hollywood star told the BBC that the levels of murder and rape convinced him ethnic cleansing was occurring.
At least 200,000 people have died in the region and some 2.5 million are homeless after three years of fighting.
The sharply deteriorating security has led to the withdrawal of 250 relief workers, leaving many vulnerable.
There are also fears that the fighting is destabilising neighbouring Chad where there has been an upsurge in violence.
The United Nations Security Council says it is gravely concerned at the situation there and has condemned attempts by rebels to destabilise the government and seize power by force.
In an interview with the BBC's Laura Trevelyan in New York, Mr Clooney said that everyone he met in Darfur told of several family members who had been victims of targeted violence.
"That's not just a war," he said.
"That is actually ethnic cleansing."
He said a larger peacekeeping contingent was immediately needed and called on all rebel factions to sign up to a May ceasefire agreement.
Mr Clooney also spoke of a recent trip to both Egypt and China - two countries which he said could do more to encourage Sudan to increase the number of peacekeepers, a proposal that Khartoum rejects.
"We think that China has quietly been doing some negotiations; Egypt has been participating in the peace process - we think they can do a lot better," he told reporters in New York.
In Washington, US Secretary of State Condoleezza Rice warned Sudan would be held accountable if it refused additional troops.
The violence has intensified despite the presence of some 7,000 African Union peacekeepers.
"The Sudanese need to be convinced that if they are not willing to accept help from the international system, then they're going to be held accountable for anything that happens," she told Reuters.
Also on Friday a group of six aid agencies said they had been forced to withdraw from Darfur because of the "unprecedented difficulties" of working in the region.
The group - which included Oxfam, the International Rescue Committee, Goal, Concern, World Vision and the Norwegian Refugee Council - said they were becoming direct targets of violence.
The conflict began in early 2003, when a rebellion by local groups triggered a counter-offensive by the army and government-backed Arab militias.