"Warring parties of South Sudan are expected to present their positions on issues related to power sharing and other affairs, which they have not reached agreement," IGAC peace and security director Tewolde Gebremeskel told The Anadolu Agency on Friday.
He said the regional bloc had given the South Sudanese rivals in November 15 days to resolve their differences and reach an agreement.
The warring parties have not presented their positions as expected and they are expected to do so at the Jan. 18 meeting, Gebremeskel said.
South Sudan has been shaken by violence since December of 2013, when President Salva Kiir accused Riek Machar, his sacked vice president, of leading a failed coup attempt against his regime.
Hundreds of thousands of South Sudanese have since been displaced in fighting between the two rivals, which has led to an increasingly dire humanitarian situation.
In recent months, the two parties have held on-again, off-again peace talks in Addis Ababa under the mandate of the Djibouti-based IGAD.
Meanwhile, Gebremeskel said that IGAD foreign ministers will meet in Somali capital Mogadishu on Saturday to discuss developments in the war-torn country.
"This indicates the existing stability in Somalia and the strength of Somalia's army and [African peacekeeping mission] AMISOM," he said.
Gebremeskel said that Saturday's meeting also reflects that terrorist groups are getting weaker and Somalia is becoming peaceful and stable.
"This makes us very happy as peace and stability in Somalia means peace and stability in IGAD countries," he said.
Somalia has remained in the grip of on-again, off-again violence since the outbreak of civil war in 1991.
Earlier this year, fractious Somalia appeared to inch closer to stability after government troops and African Union forces – deployed in the country since 2007 – drove Al-Shabaab from most of its strongholds.