The presidents of north and south Sudan are planning to meet in Ethiopia Sunday to discuss the crisis in the their border region.

African Union officials say Sudan's President Omar al-Bashir and south Sudan's President Salva Kiir will meet in Addis Ababa to discuss the disputed region of Abyei, which northern forces recently occupied.

They say Ethiopian Prime Minister Meles Zenawi and former South African President Thabo Mbeki will also participate in the talks.

Tensions between north and south Sudan flared after Khartoum sent its troops into Abyei in late May, refusing calls from the United States, United Nations and southern officials to withdraw.

U.N. officials say tens of thousands of people have fled from Abyei and neighboring South Kordofan state.

The United Nations said Friday conditions have deteriorated rapidly in South Kordofan, where civilians are getting caught between the north's Sudanese Armed Forces and the south's Sudan People's Liberation Army .

They say roadblocks have been set up, preventing humanitarian aid from getting through. They also said there are an increasing number of reports of civilians being shot and killed when they return to their homes for food and other necessities.

South Sudan voted to secede from the north in January and will officially declare independence next month.

The vote was the culmination of a 2005 peace deal between the warring sides but many issues, including a defined border and the fate of the oil-rich Abyei region, have never been decided.