The commission charged with organizing the vote on Tuesday confirmed January 9, 2011 as the date for the referendum. Observers, however, fear that the date does not give organizers enough time to properly prepare for balloting.
Southerners will choose whether to split Africa's largest country or remain in a united Sudan in the referendum. On the same day voters in Abyei, a disputed oil region straddling the country's north and south, will make the same decision for their district.
The votes are held under a 2005 peace deal that put an end to Africa's longest-running civil war between the north, which is mostly Arab-Muslim, and the mostly Christian south.
Northern and southern Sudanese leaders, however, have clashed over who is eligible to vote.
The Misseriya -- Arab nomads who use land in Abyei for seasonal pasture -- have threatened to derail the referendum if they are not granted the same voting rights as the Dinka Ngok, settled farmers seen as favorable to joining the south.
Talks between the two sides broke down in Ethiopia last week, prompting a northern official to say it would now be impossible to hold the vote as planned.
Further talks are planned in the Ethiopian capital Addis Ababa on October 27.
"With time running out, the parties must make a strategic commitment to work together to avoid war, to achieve a lasting piece," Gration said.
Both sides "must be prepared" to come to Addis Ababa "with an attitude of compromise, to reach a final agreement on these remaining tough issues.
"The entire world is watching and we'll make judgments based on how the parties approach these talks, on how they act in the next couple of months," Gration said.
Gration urged Khartoum to "transfer necessary funds to the southern Sudan referendum commission," to grant visas to international monitors and aid workers, and to "protect the southerners who are now living in the north."
Concerning voter eligibility in Abyeih, Gration said, "the parties will have to take some tough decisions. With 79 days remaining, they are going to have to work very hard and very fast to get an agreement."
US President Barack Obama "is serious about moving toward better relations with Sudan," Gration added.
Obama and UN chief Ban Ki-moon on September 24 led international warnings to Sudan that votes which could lead to the breakup of Africa's biggest nation must be held on schedule and without violence.
"At this moment, the fate of millions of people hangs in the balance," Obama told a special UN meeting.
"What happens in Sudan in the days ahead may decide whether people who have endured too much war, move towards peace or slip backwards to bloodshed."
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