The U.N. humanitarian chief urgently called on world leaders Friday to vastly increase the number of troops in Sudan's Darfur region to protect unarmed civilians and humanitarian workers facing a wave of murder, rape and looting.

Jan Egeland (search) depicted a crisis in which the number of people needing lifesaving assistance could jump from two million to four million if immediate action isn't taken.

Addressing a news conference, Egeland backed a recent U.N. report which found that war crimes and crimes against humanity had taken place in Darfur and called for the perpetrators to be sent to the International Criminal Court (search).

"The armed men in militias are getting away with murder of women and children and it is still happening. Those who direct the militias, these forces are also getting away with murder. It's impunity what we have seen taking place in Darfur," he said.

"There should be sanctions. Which ones and against whom? Not for me to decide. There should be more robust action."

Egeland said the need for more African Union troops is urgent.

"We don't have a second more to wait," he said. "This should have happened yesterday. Whatever should happen, with or without U.N. forces, let's build an African Union force now."

He also expressed fear for the safety of aid workers. "Aid workers have been killed. Our helicopters are being shot at. Our trucks are being looted. We are paralyzed," he said. "We could have provided daily bread for more than 2 million people. We are at best giving to 1.5 million people. This cannot continue."

He warned of possible famine, saying the death toll in Darfur could surpass the estimated 170,000 people killed by the Dec. 26 Indian Ocean tsunami.

Egeland criticized world leaders for leaving aid workers to apply a "band aid" instead of taking political action to resolve the conflict.

"You cannot have this kind of situation and put in 10,000 unarmed men and women with blankets and foodstuffs and field hospitals and say 'You stop this war.' We cannot. Others have to help us," Egeland said.

He said pledges for only half the $650 million needed to help the people of Darfur had been received. "We are desperately short of cash," he said.

"We're front row witnesses to more massacres. We're front row witnesses to more displacements. We are front row witnesses to massive misery and suffering of Darfur and we shouldn't be," he said.

Darfur plunged into conflict in early 2003, when rebels of ethnic African tribes took up arms, complaining of discrimination by the Arab-dominated government in Khartoum (search). Pro-government Arab militia hit back by burning villages. The war has displaced some 2 million people since it began, and claimed 170,000 lives since March.

Officials in N'Djamena, Chad, said Friday that Sudanese troops are to leave positions they seized in Darfur despite a truce. The Sudanese government has agreed to withdraw in one week and its forces will be replaced by African troops, said Gen. Mahamat Ali Abdallah, head of the commission that monitors the truce.

Also, the U.N. refugee agency said Friday it would in September start repatriating 560,000 refugees living in seven neighboring countries, but added that it has received only about one-tenth of the money needed to begin preparations.

UNHCR's Deputy High Commissioner Wendy Chamberlain told journalists in the Kenyan capital, Nairobi, that only $4 million to $5 million of the $40 million appealed for has been received.

The money is needed to build schools, clinics, provide drinking water and build roads, "so that when refugees or returnees do go back home, they don't face the kind of hardships that will lead them to leave again," she said.