For many southerners who fought decades of civil war with north Sudan to win a share of power and wealth, the 2011 ballot on whether to remain one country or secede is the main element of a 2005 north-south peace deal.
But issues of sharing oil and the river Nile waters, citizenship and demarcating a north-south border have not been discussed by north and south Sudanese officials, which one presidential advisor has called a "recipe for war".
"They can't be put on the back burner, at least serious progress will have to be made," Britain's state minister for Africa Glenys Kinnock told reporters on Wednesday in the south Sudanese capital Juba after three days of meetings.
"People will say: 'how is it going to work after the referendum if we haven't dealt with these very, very difficult and contentious issues'," she added.
Britain is Sudan's second largest bilateral humanitarian donor and the ex-colonial power.
Much lies in the year ahead, including April elections promised by the deal, which could further disrupt fragile north-south relations, plagued with outbreaks of fighting and political crises over delays in implementing the 2005 agreement.
Kinnock said that the long-delayed demarcation of the north-south border was vital, as was agreement on a fair distribution of oil revenues.
Most of the Sudan's almost 500,000 barrels per day of crude lies in the south or along the north-south border but the industry's infrastructure is all in the north.
On Tuesday, Kinnock in Khartoum warned that inter-tribal fighting in the remote and war-devastated south was a danger. An estimated 2,500 people are believed to have been killed in tribal clashes last year.
"We know that escalating violence in the south if we are realistic does have the potential to endanger the whole process," she said.
The south is awash with guns following the north-south war which claimed some 2 million lives.
With a drought damaging crops and grazing land, tit-for-tat cattle raiding looks set to continue. And a government disarmament campaign has failed to win the trust of the people, often sparking clashes between the army and civilians refusing to lay down weapons.
Cattle raids on Monday in the oil-producing Unity state killed 16 people and wounded 11, the southern army spokesman Kuol Diem Kuol said.
In the south's largest and remote Jonglei state which suffered the worst fighting last year, tribal clashes killed seven in the past four days, state governor Kuol Manyang said. (Reporting by Skye Wheeler, Editing by Opheera McDoom and Elizabeth Fullerton)
- Reuters - Thomson Reuters Foundation
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