After months of failed talks, South Sudan says relations with its former civil war foe have become 'positive', with deals concluded this week on borders and citizenship paving the way for further progress.

Newly-independent South Sudan previously accused Sudan of 'stealing' its oil during negotiations to resolve issues such as oil revenues and contested territory, leading to fears of a renewed war.

"When we were one country, we spent all the time together fighting each other and killing each other, and there has been a lot of that... but that is over now", South Sudan's top negotiator Pagan Amum told reporters on Wednesday.

"We have tried to negotiate all this time with the old approach. It has led us literally nowhere...now we are going to try this approach, which is basically positive thinking, applied to problem solving", he said on return from the last round of African Union (AU)-led talks in Ethiopia.

Amum said the new approach was already working, after the two nations inked deals to safeguard the status of each other's citizens and demarcate the oil-rich border, ahead of an April 8 deadline for southerners to leave Sudan.

The presidents of both countries are due to meet in the southern capital Juba soon to finalise the current deals and attempt to make progress on others, he added.

"We plan to make this summit successful, to sign these two agreements and other agreements between the two states, reduce the tension... and create a positive environment," he said.

"Under the initialed agreement on nationality, nationals from each state will now enjoy in the other state the following freedoms: freedom of residence; freedom of movement; freedom to undertake economic activity; and, the freedom to acquire and dispose of property," Amum said

Sudan has agreed to pay back oil it had taken, while South Sudan will hand over months of unpaid transit fees, he added.

The two nations will negotiate a commercial agreement on oil transport and transit fees first, and then a package deal on the contested region of Abyei and how much Sudan should be paid for the "financial loss of the south", he said.

South Sudan split from the north in July with 75 percent of the country's crude oil, but relies on a pipeline, refineries and port in Sudan to export it.

The new nation shut down oil production in late January, after accusing Sudan of 'stealing' oil in lieu of a transit fee that is at the centre of the dispute.

South Sudan said that it would also call for sanctions against Sudan to be lifted and for it to be granted debt relief, but added that its cash-strapped neighbour also needed to end wars with rebels in the troubled region of Darfur and in states along its new border that were allied to the southern liberation army.

"If they don't solve these problems, Sudan won't be stable," Amum said.