(CNN) -- Nearly 99% of Southern Sudanese voted to split from the north, organizers reported Sunday, marking the first complete preliminary results.
With 100% of votes counted, an overwhelming 98.83% voted to split, the Southern Sudan Referendum Commission said on its website.
Sudan's north and south have been at war for two decades in a conflict that killed 2 million people.
The referendum on whether to declare independence from the government based in the north is part of a 2005 peace agreement that helped end the conflict. The war pitted a government dominated by Arab Muslims in northern Sudan against black Christians or animists in the south.
A majority of Sudan's oil reserves are in the south, another flashpoint in the war.
Several million voters cast ballots, including expatriates in the United States and seven other countries.
The south would become a new nation in July if the vote is validated and no other obstacles emerge.
"If there is no appeal, the final results will be announced on February 7," said Justice Chan Reec Madut, deputy chairman of the commission. "But if there is an appeal or appeals, they have to be discussed, and the final announcement will then be on February 14."
The commission said it faced various challenges during the vote, including time, funding and the complexity of the law.
"The law itself was framed in an unclear way with much repetition. ... It was shaky," said Muhammad Khalil, the commission chairman.
Nevertheless, Khalil said, the referendum commission, which included southern Sudanese and northern Sudanese members, made "decisions in accord."
Khalil said the commission did not have much time to conduct its work.
"It was conceived by those who signed the Comprehensive Peace Agreement (CPA) that the referendum process would take 42 months," he said. "By the time the referendum commission was established, we had four months."
Funding was also a challenge, Khalil said.
"The international funding was generous, but not made available for Sudanese expertise," he said. "If we had more funding, we would have included more Sudanese experts to give the referendum an added national face."
Logistical difficulties included residents delivering election materials to other counties by foot, officials said.