Frantic efforts to broker a deal on festering disputes between Sudan and South Sudan made little headway Tuesday, the third day of a presidential summit in the Ethiopian capital.
The mood was initially optimistic when the leaders began talks Sunday -- in what was originally billed as a one-day meeting -- but had appeared to sour over sticking points of contested border regions and security issues.
"There has been back and forth all day, trying to find a position acceptable to both sides... Nothing is yet ruled out," a Western diplomat said.
President Omar al-Bashir of Sudan and his Southern counterpart Salva Kiir met late Tuesday for another round of direct talks alongside the African Union's chief mediator, former South African president Thabo Mbeki.
Bashir appeared stony faced as he entered the room to meet Kiir, but both smiled at each other across the table before reporters were ordered to leave.
Amid international pressure to reach a deal -- after missing a UN Security Council deadline to settle by Saturday -- teams from each side spent the day locked in efforts to narrow positions, as mediators shuttled between them.
A key stumbling block is the Mile-14 area, a contested sliver of land on the border.
Sudan's Defence Minister Abdelrahim Mohamed Hussein has said the strip "is Sudan's territory and would not be compromised", according to the Sudanese Media Centre, which is close to the security services.
Sudanese delegation official El-Obeid Morawah said Monday that "progress had been made" but did not give clear details, and similar comments were made by South Sudan's Information Minister Barnaba Marial Benjamin in Juba on Tuesday.
However, delegates on both sides were apparently pessimistic about the chance of a deal, and diplomats said they were preparing for talks to potentially extend until the end of the week.
The protracted talks under African Union mediation began in the Ethiopian capital several months before South Sudan split in July 2011 from what was Africa's biggest nation, following an independence vote after decades of war.
Key issues include the ownership of contested regions along their frontier -- especially the flashpoint Abyei region -- and the setting up of a demilitarised border zone after bloody clashes.
The buffer zone would also potentially cut support for rebel forces in Sudan's Southern Kordofan and Blue Nile regions that Khartoum accuses Juba of backing, just as the South accuses Sudan of arming rebels in its territory.
The UN set a deadline for a deal after brutal border clashes broke out in March, when Southern troops briefly wrested the valuable Heglig oil field from Khartoum's control, and Sudan launched bombing raids in response.
UN leader Ban Ki-moon has called on the leaders to tackle their remaining differences, "so that their summit concludes with a success that marks an end to the era of conflict".
Despite slow progress, both sides still appeared keen to end the conflict and a stalemate over stalled oil production that is crippling their respective economies.
A comprehensive deal -- as opposed to another stepping-stone agreement -- would have to include a settlement on Abyei, a Lebanon-sized border area claimed by both sides and currently controlled by Ethiopian peacekeepers.
But even among the most optimistic diplomats, there seemed little chance of a breakthrough to solve the growing humanitarian crises in Sudan's civil war states of Southern Kordofan and Blue Nile.
However, it was hoped the summit would settle the details of last month's deal to fix the oil export fees that landlocked South Sudan will pay to ship crude through Khartoum's pipelines to the Red Sea.
At independence, Juba took two-thirds of the region's oil, but processing and export facilities remained in Sudan. In January, the South shut off oil production after accusing Sudan of stealing its oil.