Khartoum - In the first such transfer in about a year, 1 500 ethnic South Sudanese are to return to their ancestral homeland from Khartoum area squatter camps on Saturday, the International Organisation for Migration said.
"They want to go home," Mario Lito Malanca, IOM's chief of mission in Sudan, told AFP.
The group leaving for South Sudan's Northern Bahr El Ghazal state are among almost 20 000 who the IOM says have been "stranded" in Khartoum for more than two years.
Almost every single one of them wants to go South, an IOM survey found.
Without money to travel themselves, many live in the open where cloth bags wrapped around metal crates, beds and other possessions provide crude shelters, in conditions which the UN has called "appalling."
South Sudanese have been classed as foreigners in Sudan since April last year, restricting their access to employment and services following the independence of South Sudan in July 2011.
Geneva-based IOM, to which 155 countries belong, appealed to donors in November for $10.55m to support the Sudanese and South Sudanese governments in providing "safe and dignified" transport for the 20 000 southerners in Khartoum.
However, the donors did not respond and IOM is to use its own resources to provide buses and trucks for Saturday's convoy.
The initiative is led by the governments of Sudan and South Sudan, which have agreed to provide security.
IOM is supporting the return, with help from other UN agencies and the Red Cross, to ensure people are moved "orderly, safely and humanely," Malanca said.
Tensions between the two nations, and a lack of funds, had prevented an IOM-assisted repatriation since last year.
In November, the Africa Inland Church moved about 1 600 people to South Sudan from Kosti, south of Khartoum.
That was the first major repatriation for months and followed a September summit between Sudan's President Omar al-Bashir and his South Sudanese counterpart Salva Kiir.
Their talks led to improved relations between the neighbours which intermittently clashed along their disputed border last year.
The summit affirmed the commitment of both sides to implement a series of economic and security pacts, including one for the free flow of people and goods across the frontier.
"Both governments have in fact recently confirmed their support in addressing the urgent needs of this stranded population," though they are unable to fund the entire transport costs, the IOM said in November.
Millions of Southerners fled to the north during a 22-year civil war which ended in a 2005 peace deal that paved the way for South Sudan's independence following a referendum.
About 1.8 million southerners have gone back to South Sudan since 2007, says the IOM, which in 2011 and 2012 transported more than 39 000 South Sudanese from the north.