Southern Sudan's government has drawn up plans to bring back 1.5 million displaced southerners from Sudan's north in time to vote in a January independence referendum.
The government's proposals, seen this week by reporters, are titled "Coming Home to Choose." They outline arrangements to bring the returnees home on trains, buses and boats traveling up the Nile River.
Reports vary on the budget for the program, but range upwards of $25 million.
Southern Sudan's government says it is worried there could be problems for southerners living in the north, both during and after the referendum, scheduled for January 9.
But aid agencies say they fear a sudden influx of people could be too great a burden for the impoverished region, which is still struggling to recover from Sudan's 21-year north-south civil war.
The vote is a key part of the 2005 peace agreement that ended the war and gave southern Sudan partial autonomy.
The south is widely expected to choose to secede and become an independent nation. Tensions with the north have been rising as the vote approaches.
Southern leaders accuse the north of stirring up deadly tribal violence in the region. The sides have also not resolved a long-running border dispute.
Much of Sudan's oil wealth is believed to lie along the border. The oil-rich Abyei region holds a separate referendum January 9 on whether to be part of the north or the south.
Some information for this report was provided by Reuters.