The leaders of Sudan and South Sudan are due to meet to address disputes that brought them close to war, following the independence of the south in 2011.
President Omar al Bashir of Sudan and Salva Kiir of South Sudan are set to discuss speeding up the implementation of a deal reached last September.
The talks in the Ethiopian capital Addis Ababa follow reports of renewed clashes on the disputed border.
Tensions over oil and security brought them to the brink of war last April.
Western governments have urged both sides immediately to withdraw their forces from what is intended to be a demilitarised border zone.
In September, the two men agreed to set up a demilitarised buffer zone, but some parts of the deal - such as resolving an ongoing dispute over oil - have yet to be implemented.
A BBC correspondent reports one of the most critical issues has been the halt in oil production in the land-locked South due to a disagreement over pipeline fees.