The presidents of north and south Sudan are set to meet Sunday, as fighting continues to rage along the north-south border.

Northern leader Omar al-Bashir and southern leader Salva Kiir will hold crucial talks in Ethiopia's capital mediated by former South African President Thabo Mbeki.

The African Union, which is hosting the summit, said the leaders will discuss the withdrawal of troops from the disputed Abyei region and the possible deployment of African peacekeepers.

Northern forces seized control of oil-rich Abyei last month, prompting tens of thousands of residents to flee the area.

Separately, northern troops have been fighting armed groups in the border state of South Kordofan for more than a week. On Sunday, the north's army denied reports that two of its warplanes were shot down in South Kordofan.

South Sudan is set to declare independence in less than a month, after voting to split from the north in a January referendum.

The north and south previously fought a 21-year conflict that ended in 2005. The unrest in Abyei and South Kordofan has raised fears that Sudan could plunge back into civil war.

U.S. Secretary of State Hillary Clinton is due to arrive in Addis Ababa just as the Sudanese summit is ending. Clinton, who is on a three-nation African trip, is scheduled to deliver a foreign policy address at African Union headquarters.

She is expected to meet with south Sudan President Kiir, and possibly with Sudanese Vice President Ali Osman Taha.

She will not meet with President Bashir, who is wanted by the International Criminal Court for alleged war crimes in Sudan's Darfur region.