The rival leaders of Sudan and South Sudan arrived for face-to-face talks in Addis Ababa late Friday to push for progress on stalled economic, oil and security deals, officials said.
South Sudan's President Salva Kiir and his Sudanese counterpart Omar al-Bashir arrived for the talks in the Ethiopian capital along with mediators Hailemariam Desalegn of Ethiopia and former South African president Thabo Mbeki, diplomats said.
The head of the South Sudanese delegation, Pagan Amum, said the leaders would meet Friday evening and Saturday morning.
No statement was planned after the talks late Friday.
The summit between the former civil war foes comes despite accusations from Juba on Thursday that Khartoum had launched air and ground attacks inside South Sudan.
Amum called the alleged attacks "unfortunate" and said the mood at the talks had been hampered.
"It is very definitely, negative and these (bombings) are having a negative impact on the summit and the discussions," he said.
Bashir and Kiir first met separately on Friday afternoon with Ethiopian Prime Minister Hailemariam Desalegn and African Union mediator Thabo Mbeki, the former South African president, according to diplomats and an AFP reporter.
The summit of the leaders, whose nations are both struggling with economic austerity cuts following Juba's halting of oil exports through Sudan's pipelines, is the latest of repeated rounds of African Union-mediated talks.
AU chief Nkosazana Dlamini-Zuma said Friday she hoped the summit would "enable the two presidents to agree on the best means and ways of overcoming the challenges" of implementing deals inked in September.
Juba has accused Khartoum of a series of attacks -- regularly dismissed by Sudan -- ever since the two nations came close to all-out war in March and April last year, when their armies fought bitter battles over their disputed frontier.
The leaders are meeting for the first summit since they signed security and oil agreements three months ago that have yet to be implemented.
Amum said his president was "hopeful" that both sides would agree on how to implement a series of deals signed in September, and said talks would also focus on the disputed Abyei region and border demarcation.
"We are here to see an expedited implementation of the (previous) agreements and a resolution of the outstanding, remaining issues of Abyei and the border," Amum told reporters.
The United States, Britain and Norway issued a joint statement ahead of the talks calling for a settlement, urging the armies of both nations to "immediately withdraw" from their frontier.
The resumption of oil production would be "particularly valuable for both economies and should not be held up by negotiation on other issues", they added.
Along with a demilitarised border buffer zone, the September pacts allowed for a resumption of South Sudanese oil exports through Sudan. They also said border points would be reopened for general trade.
The meeting also aims to "find solutions to the pending issues of the Abyei area", the flashpoint Lebanon-sized region claimed by both Khartoum and Juba, Dlamini-Zuma added in a statement.
The AU has proposed that if a deal is not struck on Abyei, the matter would be referred to the UN Security Council.
However, Sudanese Foreign Minister Ali Karti said that referring Abyei to the UN would "not help bring about peace", according to the Sudanese Media Center, which is close to the security services.
Sudan has made no comment on the reported clashes, but the state-run SUNA news agency said Bashir would meet with Kiir "to speed up implementation of the cooperation agreements".
South Sudan separated from Sudan in July 2011 under a peace agreement that ended a 1983-2005 civil war, but key issues including the demarcation of hotly contested border zones remain unresolved.
Khartoum also accuses South Sudan of supporting rebels operating in Sudan, which has been a major obstacle to implementing the agreements.
The South, in turn, says Sudan backs insurgents on its territory, a tactic it used to deadly effect during the two decades of civil war.