U.N. Secretary-General Kofi Annan visited the troubled Darfur region of western Sudan Thursday to consider ways to end the humanitarian crisis. More than a million people have been displaced in Darfur because of violence that human rights groups blame on government-backed militias.

Kofi Annan spoke with tribal and women leaders about the problems facing refugees in a camp called Zam-Zam, outside the city of El-Feshir. The leaders said they were afraid to return home because of possible attacks by the Janjaweed militias. But overall, they said, aid groups were looking after them relatively well in the camp.

From there, the secretary-general and his delegation went to a camp just 30 minutes away where aid workers said the security and living situation was more desperate. But the refugees were nowhere to be found.

U.N. officials said some 4,000 refugees, called internally displaced persons, or IDPs, had been in the camp the night before but they had been moved by Sudanese authorities. Jan Egeland, the U.N.'s undersecretary-general of humanitarian affairs, said the U.N. did not appreciate the authorities' actions. "It was in our program actually to show the secretary-general and the secretary-general wanted to see how IDPs live when there [are] no services," he said. "And this was such a place."

Mr. Egeland was then asked if this was a deliberate ploy by Sudanese authorities.

"I'm sure it has happened before and I'm sure it will happen again," he said.

The refugees moved to another camp are among the one million people in Darfur driven from their homes by Janjaweed militias.

Human rights groups charge that the ethnic-Arab militias have been used by the government to terrorize the Darfur's civilian population, which is ethnic-African, as part of efforts to put down an armed rebellion.

Sudanese authorities deny supporting the Janjaweed and say they are working to disarm them. Until recently, they allowed little access to the region by aid workers.

The conflict has given rise to what the U.N. calls the world's worst humanitarian crisis today. Refugees face hunger, epidemics and continued attacks in camps in Darfur or over the border in Chad.

From Darfur, Mr. Annan flew to Chad's capital, Ndjamena, for more discussions on the Darfur crisis. He is expected to return to Sudan's capital, Khartoum, Friday.