James Wani Igga, speaker of south Sudan's parliament, also urged the international community not to "go to sleep" and neglect the landmark 2005 peace deal that ended a long-running conflict between the north and the south of the country.

He told Reuters late on Tuesday that while an agreement was reached in December to resolve a political deadlock between the former northern and southern foes, little has been implemented on the ground.

"It is very difficult really to promise you that it (the census) is going to be on track," Igga said. Already delayed twice, it is now slated to begin on April 15.

"A small amount has been paid but that is not all the money that is needed," he said. This could delay the census because it had not been possible to buy vehicles or hire and train staff.

May to September is rainy season in south Sudan and many areas are out of reach by road, making a census impossible. Elections are due next year under the north-south accord known as the Comprehensive Peace Agreement (CPA).

But Igga said the northern National Congress Party (NCP) had agreed to reinsert questions in the census on ethnicity and religion, issues that fuelled Africa's longest civil war.

Claiming 2 million lives, the conflict pitted Khartoum's Islamist government against mainly Christian and animist southern rebels. The southerners rejected Khartoum's policy of Arabisation and Islamisation during the conflict, which was complicated by disputes over oil resources.

'NOTHING VISIBLE'

The SPLM froze its participation in the national coalition government in October in protest at the NCP's reluctance to implement the peace deal. The two sides later agreed to fund the census, withdraw northern troops from the south and demarcate the border before the south rejoined the government.

"But so far nothing visibly has been resolved on the ground except for the issue of the Sudan Armed Forces redeployment ... although it has not been 100 percent so far," Igga said.

He said the most important priority for the international community, distracted from the CPA by a separate conflict in Sudan's western Darfur region, was to refocus on the CPA through the Assessment and Evaluation Commission (AEC), of which he hoped Britain would take over the chair.

The AEC was set up to monitor the CPA and bring donors, the SPLM and the NCP together regularly to discuss progress.

"They (should not) relax that they already succeeded as the international community to bring peace and go to sleep," Igga said after meeting Britain's minister for Africa, Mark Malloch Brown. "The implementation is most important."

Malloch Brown said the AEC could help improve transparency in the south, where allegations of corruption are rife and the SPLM accuses the NCP of not giving them their fair share of half the revenues from oil output of at least 500,000 barrels a day.

"People here ... clearly are deeply suspicious as to whether they are getting the resources they deserve," he told Reuters.

The minister said the AEC could also be a forum for the former foes to talk frankly and not "politically grandstand".

He said action was needed now to support the CPA ahead of the elections in order to avert a return to war, which would be a disaster for the region.

Britain has promised over $100 million to develop Sudan in 2008, almost a quarter of the total bilateral pledges.