Negotiators for Sudan and South Sudan have held their first talks since deadly border fighting last month, amid fresh accusations by the South of air attacks by Sudan.
Teams from both sides are in the Ethiopian capital, Addis Ababa, for African Union-led talks which were stalled by heavy clashes last month, the worst fighting since the South won independence last July.
Idriss Mohammed Abdel Qadir from Khartoum and Pagan Amum from Juba began Tuesday's talks mediated by former South African President Thabo Mbeki, and also attended by the US special envoy on Sudan, Princeton Lyman.
Sudan stressed on Tuesday its "commitment to reach a negotiated settlement to all issues of differences" and promised "its full adherence to peace and stability between the two countries", it said in a statement released as talks began.
Sudan said it hoped the talks would mark a "new chapter" in relations "away from conflict and warring".
Al Jazeera's correspondent Harriet Martin reporting from Khartoum said that there was a cautious sense of optimism among those involved in the talks.
"The difference this time is that the international community has pushed the two sides back to the table very clearly with [the] UN resolution [in mind]".
Security Council warning
The UN Security Council earlier this month ordered both sides to cease fighting and return to talks or face possible sanctions.
However, the talks in Addis Ababa were overshadowed by claims by South Sudan that Sudanese fighter jets bombed border areas in three Southern states - Unity, Western and Northern Bahr el Ghazal - for the fourth straight day.
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"Today as we speak they bombed us," Amum said just hours before the talks started. Nevertheless he said the talks would resume on Wednesday and that he was optimistic they would produce results.
Sudan has denied attacking the South, and the raids could not be confirmed independently.
Sudan has in turn accused the South of alleged cross-border incursions, which it said broke the UN order to halt hostilities.
Sudan, in an apparent peace gesture, reported it had pulled out troops from the contested Abyei region to end a year-long occupation, an area whose ownership is vital for both South Sudan and Sudan.
A UN spokesman confirmed the pullout, which was in line with a UN Security Council demand for both sides to demilitarise the territory.
Abyei is one of the main disputes between Sudan and South Sudan, which have been fighting each other along their uncharted border.
Sudanese troops stormed the region in May 2011, forcing some 110,000 people to flee southwards, where the majority remains in impoverished camps.
"SAF (Sudanese Armed Forces) deployed out of Abyei area this evening and they gave the military compound there to UN peacekeepers," according to the Sudanese Media Centre (SMC), which is close to the security apparatus.
Diplomatic sources said the pullout involved about 300 troops.
"We declared yesterday that we're going to redeploy so we are going to do whatever we declared," Abdel Qadir, Khartoum's negotiator, said as talks broke for the night late on Tuesday, refusing to comment on the progress of discussions.
However, Amum rejected Sudan's reported pullout, claiming "Sudan did not withdraw from Abyei ... up to today they are still in Abyei".
Abyei was to have held a referendum in January 2011 on whether it belonged with the north or South, but that ballot was stalled over disagreement on who could vote.
South Sudan broke away from Sudan in July after a 2005 peace deal ended one of Africa's longest civil wars, which killed about two million people.
But tensions soon flared again over a series of unresolved issues, including the border, the future of disputed territories and oil.
The South separated with about 75 per cent of the former united Sudan's oil production, but it still depends on the north's pipeline and Red Sea port to export its crude.
A protracted dispute over fees for use of that infrastructure led South Sudan in January to shut its oil production after accusing the north of theft.
Salva Kiir, South Sudan's president, said before Tuesday's talks that "amicable dialogue on the outstanding issues with Khartoum is the only option for peace".