Ballots were counted on Wednesday in the referendum in the flashpoint Abyei region to decide if it lies in Sudan or South Sudan, observers said, amid African Union warnings the poll is a "threat to peace".
The fate of Abyei is one of the most important and sensitive issues left unresolved since South Sudan became an independent state in 2011, ending two decades of civil war in Sudan.
"It is a laborious process of counting the number of ballots but it is going on slowly but surely," said Tim Flatman, an independent observer in the disputed district, saying initial observations suggested a "very transparent process".
The majority of 65 000 registered voters are believed to have cast their ballots in the three-day long poll which closed Tuesday evening.
Preliminary results were expected later on Wednesday or on Thursday, but organisers were struggling to reach some more remote parts with vehicles making slow progress to get through on mud tracks.
AU chief Nkosazana Dlamini-Zuma has said the vote was illegal and its organisers were risking sparking a return to war between civil war foes in Juba and Khartoum.
"They pose a threat to peace in the Abyei area, and have the potential to trigger an unprecedented escalation on the ground … with far-reaching consequences for the region as a whole," she said in a statement on Monday.
Patrolled by some 4 000 Ethiopian-led UN peacekeepers, the area is home to the settled Ngok Dinka tribe, closely connected to South Sudan, as well as the semi-nomadic Arab Misseriya, who traditionally move back and forth from Sudan grazing their cattle.
Only the Ngok Dinka are voting in the referendum – although organisers insist it was open to all residents – and the Misseriya have already angrily said they will not recognise the results of any unilateral poll.
Ballots cast are therefore expected to overwhelmingly support Abyei joining South Sudan.
Abyei was meant to vote on whether to be part of Sudan or South Sudan in January 2011 – the same day Juba voted overwhelmingly to split from the north – as part of the 2005 peace deal which ended Sudan's two-decade long civil war.
That referendum was repeatedly stalled, and Sudanese troops stormed the Lebanon-sized enclave in May 2011 forcing over 100 000 to flee southwards, leaving a year later after international pressure.
Analysts have warned the poll could trigger fresh violence.
"Even if the initial declaration of the referendum results does not lead to clashes, the upcoming annual [Misseriya] migration will present a stiff test to both sides," said a report by the Small Arms Survey, a Swiss-based independent research project, adding that "people of Abyei are deeply frustrated".
Zacharia Diing Akol, of the South Sudan's think tank the Sudd Institute, warned of a "potentially explosive, precarious situation", noting that Khartoum and Juba have fought over the enclave in 2008 and 2011.
Both Khartoum and Juba have criticised the vote saying they will not recognise it.
"The Ngok Dinka political leadership is aware that neither country will accept the results of the referendum," the Small Arms Survey said, but added that the "high-risk strategy" of the vote "is the one thing that the Ngok Dinka community can do for itself". – AFP