Leaders of the two nations had been scheduled to meet Tuesday in South Sudan’s capital Juba, but Sudanese President Omar al-Bashir pulled out.

Crisis talks backed by the African Union are set for Saturday in Addis Ababa, to be mediated by former South African president Thabo Mbeki.

“President Zuma called on both parties not to undertake any action that would undermine the security and stability of the region and each other’s territories,” the foreign ministry said in a statement.

“Furthermore, President Zuma has called on his dear brothers, President al-Bashir and President Salva Kiir, to resume their scheduled talks and ensure that the summit in Juba takes place as planned,” it said.

“The summit would be a strong gesture and have a calming and restorative effect on the relations,” the statement added.

“This recent military confrontation has the potential to worsen the humanitarian crisis in the affected region, leading to further civilian casualties, and also threatens to precipitate a resumption of conflict between Sudan and South Sudan.”

Each side accuses the other of starting the fighting, the worst violence since South Sudan’s independence from Khartoum after decades of civil war.

South Sudan said northern bombers and troops had struck first on Monday, moving into Unity state before Southern troops fought back and took the Heglig oil field, parts of which are claimed by both countries.

Sudan later recaptured the field.