The presidents of Sudan and South Sudan are to meet Tuesday in the south's capital of Juba to try to reduce tensions between the two neighbors.
Officials from the north say Sudanese President Omar al-Bashir and South Sudanese President Salva Kiir will discuss the disputed oil-rich region of Abyei.
The status of that region is one of several issues that have strained relations between the two countries since the south seceded from the north in 2011. Abyei was to hold a referendum that year to determine whether it would be a part of the north or south, but the vote did not take place.
A member of Sudan's ruling National Congress Party told VOA the two countries have not yet reached an agreement to create a stable environment necessary for the referendum. He said Sudan will not support a unilateral decision by South Sudan to hold a referendum.
Sudan says the vote should not include the Misseriya nomads who pass through the disputed territory on their way to grazing grounds for their cattle.
Relations between the former civil war foes have been strained, occasionally flaring up into hostilities. Last year, the countries almost went to war over which side controls Abyei.
The two countries also have had disputes over oil, which is pumped in the south but refined in the north.