The government split the western region into three states in 1994, and then later into five states, following years of fighting in which mainly non-Arab tribes took up arms against what they said was discrimination by the Arab-led administration.

Major rebel and opposition groups, who boycotted the government-arranged referendum, believe the splitting up of the region led to heavier Khartoum control and helped trigger renewed fighting in 2003.

But the state referendum commission said on Saturday that 97% of voters chose to continue with the multi-state administrative system and that 3.08mn people of a total 3.21mn eligible voters had turned out, figures that opposition groups said were fraudulent.

"These results reflect the fraud the Sudanese government continues to employ in all of its elections. It's the falsification of the will of the masses," said Jibril Bilal, a spokesman for the Justice and Equality Movement (JEM), one of Darfur's two main rebel groups.

"These results are not real nor logical. We don't acknowledge the referendum, which most of Darfur boycotted," he added.

According to the UN, some 300,000 people have been killed in Darfur since the conflict first began, while 4.4mn people need aid and more than 2.5mn have been displaced.

The government presented the April 11-13 referendum as a major concession, while opposition groups say a vote should be held only after a political settlement is reached to the intermittent 13-year conflict.

Although violence has eased in recent years, an insurgency continues and Khartoum has escalated attacks on rebels over the past year. At least 130,000 people have fled fighting in the central Jebel Marra area since mid-January alone.

"A referendum held this way complicates the situation in Darfur. We and the rest of the revolutionary forces demand the return of Darfur to a unified system, as it was before," Bilal said.

Analysts and diplomats say the government opposes a unified Darfur as this would give the rebels a platform to push for independence just as South Sudan did successfully in 2011, taking with it most of the country's oil reserves.