But with a January peace deal at least solving the largest and longest-running of those conflicts in the south, the UNHCR would begin a voluntary repatriation programme back to southern Sudan after the local rains, he said.

Other UNHCR officials confirmed that would be in October.

"We hope that after the rainy season we will be able to start a movement of coordinated return from Congo, from the Central African Republic, hopefully also from Kenya and Ethiopia, to southern Sudan," Guterres said.

"There are few operations in the past that have been bigger than this one," he added, citing Afghanistan as one.

Guterres said refugees would obviously not return to dangerous areas where Ugandan Lord's Resistance Army (LRA) rebels or Sudanese militia still operated.

"This is not easy, there are still some pockets of instability in southern Sudan."



WORLD MUST PUSH FOR DARFUR PEACE

Preparation for returning refugees was underway in southern Sudan including some building of schools, health centres and wells, as well as de-mining after two decades of war, he said.

In countries hosting refugees, registration of refugees was being done, then there would be an information campaign before the Sudanese were offered the chance to go home.

An estimated 20,000 had already begun trekking home spontaneously, encouraged by peace in the south, Guterres said.

Perhaps the biggest challenge, the UNHCR boss said, was to create basic infrastructure in the vast, remote and under-developed south, which is about half the size of Western Europe with a population of around 10 million.

"During centuries very little has been done in southern Sudan. We have not a problem of reconstruction. We have effectively a problem of construction," he said.

Guterres lamented that the international community had taken its eye off conflict in Darfur, which has killed tens of thousands of people and forced more than 2 million from their homes since early 2003.

A sixth round of talks between Darfur rebels and the Khartoum government is scheduled for mid-September.

Guterres said there was "political will" on both sides to resolve the conflict -- which some have called a "genocide" by Khartoum-backed Arab militia -- but little time left.

"It is essential for the international community to pressure for this political will to be translated into real peace agreements to be effective until (by) the end of this year. This is a window of opportunity we cannot neglect," he said.

"Without peace we can only face a new tragedy of proportions that cannot even be imagined."

[ENDS]