Sudanese President Omar al-Bashir landed on Tuesday in Juba, where he is to hold rare talks with South Sudanese President Salva Kiir.
The two are likely to discuss the disputed area of Abyei, lying along the countries’ shared border.
The region was meant to hold a referendum on its final status, but so far no vote has been organised.
The African Union in 2012 had proposed a referendum for this October.
The countries are also still locked in disputes over the sharing of oil revenue.