The leaders of Sudan and South Sudan met late on Friday to try to defuse hostility that has simmered since the south broke away in 2011 and restart cross-border oil flows to rescue their crumbling economies.

No details emerged as Sudan's Omar Hassan al-Bashir and South Sudan's Salva Kiir met in the presence of Ethiopian Prime Minister Hailemariam Desalegn who is trying to mediate between the neighbors who came close to war in April.

Both leaders will meet alone for the first time at a summit on Saturday, Sudan's state news agency SUNA said.

North and south already agreed in September to resume oil exports and secure the volatile border but they failed to follow through as mistrust lingered, a legacy of one of Africa's longest civil wars.

Analysts say the confrontation helps shore up the domestic popularity of both governments by diverting attention from their economic problems and widespread corruption.

But the neighboring economies rely heavily on energy revenues and need the oil to flow again from the fields in South Sudan. The southern government in Juba shut down its entire output of 350,000 barrels a year ago after failing to agree on an export fee.

The north charges the south millions of dollars a month to pipe the crude through its territory and export it via a terminal on the Red Sea.

Under the September deals, they agreed to pull back their armies from the border stretching for almost 2,000 km (1,200 miles), much of which is disputed.

Both sides say such a buffer zone is necessary before oil from the landlocked south can flow through Sudanese territory.

On Friday, South Sudan's chief mediator Pagan Amum accused Sudan of dropping bombs across the border four times this week. Sudan's army was not immediately available for comment but routinely denies such claims.

"It is very, definitely, negative. These (air strikes) are having a negative impact on the summit and discussion," Amum told reporters in Addis Ababa.

In turn, Sudan regularly accuses South Sudan of supporting rebels of the Sudan People's Liberation Movement-North (SPLM-North) in two border states. Juba denies the accusation and says Sudan is backing militias on its territory.

Diplomats say both sides tend to see such summits as an opportunity to pick away at the other's weaknesses rather than an opportunity to solve their conflicts.

(Reporting by Aaron Maasho; Writing by Ulf Laessing; Editing by Tom Pfeiffer)