Preparations have already begun for a referendum that will take place in 2011 to decide whether Sudan should split in two.
The oil-rich south is seeking autonomy from the Khartoum government in the north.
Southerners will have the chance to vote for secession in the referendum but there is confusion over the rights of those who fled to the north during the country’s 22-year civil war.
They are being told they will have to return home if they want to vote.
Al Jazeera’s Mohammed Vall reports from Khartoum.