"The Secretary-General is returning to Darfur to see firsthand one of the world's worst humanitarian crises and the progress being made in meeting the people's needs on the ground," said UN spokesman Stephane Dujarric, who said Annan was due in to arrive in the Sudan on Friday.

"By going to Darfur, he hopes to rally support for the AU's (African Union's) security presence, revitalize the AU-mediated political process, and focus attention on the need to sustain the vital and massive UN-led humanitarian assistance activities underway there," Dujarric said.

The visit will be the second to Darfur by the UN secretary general, who first traveled there last summer.

Before traveling to Sudan, Annan was to stop in Ethiopia where he was to co-chair a donors' conference to help bolster the AU's peace force in Darfur. An African Union force monitors the fragile ceasefire in Sudan's western region.