South Sudan’s President Salva Kiir said Khartoum was delaying demarcating the north-south border to try to retain control over oil reserves with Sudan’s elections just days away.

Analysts say a failure to resolve the border issue between the former north-south foes could spark renewed conflict if the problem is not sorted before Africa’s largest country holds a January 2011 referendum on independence for the south.

On Tuesday Kiir’s ex-rebel Sudan People’s Liberation Movement (SPLM) said it would boycott Sudan’s April 11 national elections accusing Khartoum of widespread fraud.

“Why it is not demarcated is because there is oil and the north wants to take the oil, they want also to take the agricultural land we have so it becomes their land,” Kiir told voters at a rally in the southern Lakes State.

Sudan’s potential 500,000 barrels per day of oil from wells mostly in the south inflamed a 22-year-long civil war between the SPLM and the northern National Congress Party which ended with a 2005 peace deal.

Under the accord south Sudan receives about 50 percent of government oil revenues from wells in the south but the opaque distribution of cash has been a source of much contention. Oil revenues accounts for an estimated 98 percent of semi-autonomous south Sudan’s budget. Many of the oil fields lie on the north-south border.

Analysts say the north-south border demarcation is key to successful talks between the two sides on post-referendum wealth sharing of oil and water from the River Nile.

Hundreds of supporters greeted Kiir on the campaign trail for the south Sudanese presidency, waving banners and kicking up dust in celebratory dances in the small Yirol town, which has few permanent buildings like much of the south devastated by the war. Several white bulls were slaughtered in his honour.

The SPLM said it would boycott all elections in the north on Tuesday, except the central states of Blue Nile and South Kordofan, where it said it was sure to win, despite the widespread fraud they accuse the NCP of committing.

The move has sparked confusion among Sudan’s opposition. Some have also boycotted but others are continuing in the race, although they all agreed with the concerns over irregularities.

Kiir also accused Sudan’s President Omar Hassan al Bashir of refusing to form commissions to oversee the southern referendum and another vote for the citizens of the oil-rich Abyei area to choose whether to join the north or south.

“They don’t want the south to stand alone,” he said, speaking in his native Dinka, the language of the south’s largest tribe. “The intention is to take over the land so they will control everything.”

Lakes state is largely flat scrub land dotted with big palm trees but also has wetlands, valuable to the resident pastoralist tribes whose armed young men battle in deadly cattle raids through the dry season.

(Editing by Opheera McDoom and Matthew Jones)