The United States had declared the peaceful conduct of South Sudan's January independence referendum a top priority and offered the Khartoum government a 'road map' to full ties if it allowed the vote to proceed and made progress on Darfur.

While Washington has praised Sudan for the January vote, officials have said they are still concerned about the situation in Darfur, where violence continues.

"We have delivered what we promised. We now want all sanctions to be lifted," Foreign Minister Ali Karti told Reuters on the sidelines of an African Union summit in Ethiopia.

"Darfur should not be attached on this. We are providing our full cooperation with them to solve the issue," he said.

Karti hoped the peaceful conduct of the vote would provide an opening for economic opportunities for his isolated country, which has long faced embargoes.

"We want more investment in our country. We want to strengthen our trade and enhance cooperation on all aspects," he told Reuters.

The United States has so far taken some small initial steps to lift export controls on agricultural machinery to help Sudan's struggling food sector, but has stressed that further progress is contingent on Khartoum's continued cooperation.

The United Nations estimates 300,000 people died in a humanitarian crisis following a government counterinsurgency campaign in Darfur in 2003 that Washington branded as genocide. Khartoum puts the figure at 10,000.

The referendum earlier this month was promised in a 2005 peace deal which ended decades of north-south conflict, Africa's longest civil war, which cost an estimated 2 million lives.

According to the terms of the accord, south Sudan will be able to declare independence on July 9, pending any legal challenges to the results.

Northern and southern leaders have still not reached a deal on their shared border, how they will split oil revenues after secession and the ownership of the disputed Abyei region.