Sudan's parliament on Tuesday passed a long-awaited bill setting out the conditions in which a January 2011 referendum on independence for the country's oil-producing south would be considered to be valid.
MPs from the former rebel Sudan People’s Liberation Movement (SPLM) and other southern parties withdrew from the parliamentary session in protest at a clause that would allow diaspora southerners to cast absentee ballots.
According to the bill, 60 percent of the southern Sudanese electorate will have to turn out to make the referendum legitimate. South Sudan will split away from the north if more than half of voters choose independence.
SPLM deputy secretary general Yasser Arman called the vote a breach of a 2005 power-sharing accord and threatened a boycott of parliament until the legislation was revisited.
"What happened today is the worst violation against the Comprehensive Peace Agreement, and from today we will not participate in parliamentary sessions until this matter is resolved," he told a media conference.
"How can the parliament approve the law for the referendum for South Sudan without the participation of representatives from South Sudan?" he added.
Analysts warn the south could return to war if there is any sign Khartoum will not go through with the vote and that would have a devastating impact on the country, its oil industry and stability in the region.
"Finally, after a long journey, we approved this law," said parliamentary speaker Ahmed Ibrahim al-Tahir who is a member of the National Congress Party (NCP) which dominates the north.
After months of wrangling, leaders from the SPLM and NCP agreed on the bill’s terms in a series of late night meetings this month.
South Sudan secured the independence vote, due in January 2011, as part of a 2005 peace accord that ended two decades of civil war with the north that killed 2 million people.
Many southerners, embittered by years of bloodshed, are thought to favor independence. Leaders from the SPLM have been making increasingly separatist public comments in recent months.
Secession would mean Khartoum would lose control of most of the country’s proven oil reserves, predominantly found in the south, though the landlocked south is dependent on northern pipelines to carry its oil to Port Sudan on the Red Sea.
Sudan’s north and south are split over differences in ideology, ethnicity and religion. North Sudan is mostly Muslim while southerners are largely Christian and followers of traditional beliefs.