Sudan and South Sudan were set to resume security talks late on Sunday, with Khartoum demanding that its southern neighbour cut ties with rebels on its territory.
The two nations signed agreements in September to secure their disputed border and resume oil exports from the south after clashes brought them close to full-scale war in April.
It was the worst violence since the South seceded last year under a 2005 peace deal that ended decades of civil war.
But neither has yet withdrawn its army from the border and the oil vital to both economies is still not flowing from fields in the landlocked south through the north.
Officials from both sides told Reuters their respective defence ministers were in the Ethiopian capital alongside other senior officials and talks were due to begin late on Sunday.
South Sudan shut down its output of 350,000 barrels a day in January after failing to agree on an export fee with Sudan.
Earlier this month, Sudan's Second Vice President al-Haj Adam Youssef told Reuters that Sudan would not allow South Sudanese oil exports to flow through its territory until Juba cuts links with insurgents and expels their leaders, dampening hopes of a quick restart after the September deals.
Khartoum has long accused South Sudan of supporting the SPLM-North - insurgents fighting in two Sudanese states bordering South Sudan - as well as other rebels in the western Darfur region. Juba denies the charges.
On Friday, the African Union urged Sudanese President Omar Hassan al-Bashir to meet his southern counterpart Salva Kiir "in the shortest possible time, in order to remove bottlenecks on all pending issues".
The rivals are also at odds over Abyei, a contested area between Sudan and South Sudan prized for its fertile grazing land.
The U.S. special envoy for Sudan and South Sudan Princeton Lyman said on Friday he was "troubled" by the delay in implementing the September deals, which he blamed on "new requests and demands" by Khartoum.