| South Sudanese officials say recent meetings in Khartoum have led to little progress on the referendum [Reuters]
Sudan is a "ticking time bomb" in the run-up to a scheduled January vote on independence for the country's oil-rich south, Hillary Clinton, the US secretary of state, has said.
She said it was "inevitable" that the south would vote to break away and form an independent state.
She told an audience at the Council on Foreign Relations on Wednesday that the US, the African Union and other international partners are trying to ensure the vote goes smoothly.
"The [north-south] situation is a ticking time bomb of enormous consequence," Clinton said.
"The south is not quite capable of summoning the resources to do [the referendum], and the north has been preoccupied and is not inclined to do it, because it's pretty clear what the outcome will be."
The referendum would be the capstone of a 2005 peace agreement between the government in Khartoum and the Sudanese People's Liberation Movement (SPLM), the main opposition group in the south.
But preparations for the vote have languished: The commission organising the ballot still has not set a date for voter registration. A coalition of NGOs warned in July that the government is "alarmingly" unprepared for the vote.
"The real problem is, what happens when the inevitable happens and the referendum is passed and the south declares independence," Clinton said. "What happens to the oil revenues? ... This is going to be a very hard decision for the north to accept."
SPLM officials have held a number of recent meetings with their counterparts in Khartoum to discuss the vote.
Officials from the south have been pessimistic about the outcome of those meetings: Yasir Arman, a senior member of the SPLM, accused the north of trying to "buy time" and delay preparations for the vote, according to the Sudan Tribune.
John Andruga Duku, a former ambassador from south Sudan to Kenya, told the Voice of America that the electoral commission was delaying the launch of a voter education programme.
Khartoum has struck a more optimistic tone: Sudan's official Suna news agency reported on Wednesday that Clinton calle Ali Osman Muhammad Taha, the vice-president of Sudan, and expressed "relief over the progress made on the referendum issues".
Taha promised that the ballot would be held on time, according to the SUNA report.
The UN plans to hold a high-level meeting on Sudan during its General Assembly meeting later this month.
Susan Rice, the US ambassador to the UN, said on Wednesday that Barack Obama, the US president, plans to attend the meeting.
"[He] sees this meeting on [September 24] as a very important vehicle for focusing international attention on the referendum," she said.