The presidents of Sudan and South Sudan have agreed to set up a demilitarized border zone and resume oil exports, but left several major security questions unresolved, according to news reports.

According to VOA News, Sudanese President Omar al-Bashir and South Sudanese President Salva Kiir plan to sign the deal on Thursday in Addis Ababa, Ethiopia. African Union mediators had decided to extend the ongoing summit between Sudan President Omer Al-Bashir and his South Sudanese counterpart Salva Kiir Mayardit until Friday after another round of lengthy talk made little headway.

"There is agreement on some areas," said South Sudan delegation spokesman Atif Kiir told AFP, while his Sudanese counterpart Badr el-din Abdullah Badr spoke of "progress on many issues". One such issue is who controls the fertile Abyei region, along with other border crossings.

AFP reports that few details of the agreement were released but that both coutries said a demilitarised border buffer zone - where troops must withdraw 10 kilometres from the de facto line of control along the undemarcated frontier - had been agreed.

South Sudan, which declared independence in July 2011, cut off oil exports through Sudanese pipelines in January of this year after a disagreement about transit fees.

The dispute cut off oil revenue to both countries, threatening their already fragile economies.

The presidents were under international pressure to reach a deal - including a threat of sanctions from the United Nations.