Sudan President Omar al-Bashir has warned that Southern Sudan will face instability if it votes to secede from the north in a forthcoming referendum.
He told al-Jazeera TV the south did not have the ability to create a stable state or provide for its citizens.
The BBC’s James Copnall in Khartoum says the comments will infuriate the SPLM – ex-rebels who have ruled the south since civil war ended in 2005.
Final rallies have taken place in the south before voting starts on Sunday.
Correspondents expect an overwhelming “yes” vote, which would see the world’s newest country come into being.
The referendum is part of a 2005 deal that ended the two-decade north-south civil war.
In an interview with the Arabic news channel al-Jazeera, Mr Bashir said he understood why many southerners wanted independence, but he expressed concern at how the new nation would cope.
“The south suffers from many problems,” he said.
“It’s been at war since 1959. The south does not have the ability to provide for its citizens or create a state or authority.”
Mr Bashir said southerners living in the north would not be allowed dual citizenship, and floated the idea of the two nations joining in an EU-style bloc.
He also raised the issue of Abyei, an oil-rich region with disputed borders.
He warned that if southerners seized the region for themselves, it could lead to war.
Analysts say Mr Bashir is under intense pressure from northern politicians, who fear that secession of the south may lead to a further splintering of the country.
North and south Sudan have suffered decades of infighting in conflicts driven by religious and ethnic divides.
Southerners have long complained of mistreatment at the hands of the Khartoum government.
At an event on Friday, former South African President Thabo Mbeki – the African Union’s mediator on Sudan – said the vote marks the “true emancipation” of the people of the south.
“The work of freedom is just at its beginning. We are confident that the southern Sudanese people have the strength and spirit to succeed in that endeavour,” he told a large crowd in Juba, the south’s capital.
Southern Sudanese will have a week to cast their vote on the future of the region, one of the least developed areas in the world.