Sudan and South Sudan vowed Wednesday to step back from the brink of all out war after three days of border violence including airstrikes and tank battles prompted international concern of a wider conflict.

Fighting on the ground had reportedly ceased on both sides of the undemarcated border but dead bodies and destroyed tanks lay strewn in Sudan's contested oil centre of Heglig, the site of bloody battles that began Monday.

Both Juba and Khartoum said senior envoys would meet in the Ethiopian capital Thursday in a bid to stave off further violence.

"What we expect to achieve is the cessation of hostilities," South Sudan's top negotiator Pagan Amum said. "We will stop the fighting that is there, and ensure that this does not erupt into war between the two countries."

Sudanese foreign affairs official Rahamatalla Mohamed Osman, who had arrived in Addis Ababa ahead of the talks, said Khartoum did not want a war with the South, but warned "if they want to accelerate, we will defend ourselves."

Sudanese warplanes on Monday launched air raids on newly independent South Sudan, while the rival armies clashed in heavy battles.

Both sides claim the other started the fighting, the worst since South Sudan declared independence from Khartoum last July after decades of civil war.

The African Union, UN Security Council and European Union have called for an end to the violence, while US Secretary of State Hillary Clinton said Khartoum bore the responsibility for the renewed hostilities.

The pan-African body said Wednesday it was deeply concerned at an "escalating security situation" on the border between the former civil war foes, and called for troops to pull back 10 kilometres (6 miles) either side of the border.

The unrest jeopardises AU-led efforts to resolve contentious border and oil disputes that have ratcheted up tensions between Juba and Khartoum.

The last round of AU-mediated talks in Addis Ababa closed this month with an agreement on nationality and border issues, which was hailed as a major breakthrough in dragging negotiations, but the mood has soured since.

Juba said northern bombers and troops had struck first on Monday, moving into Unity State before Southern troops fought back and took the Heglig oil field, parts of which are claimed by both countries.

Sudan later retook the field.

"Heglig and all around it is completely secure," Bashir Meki, the Sudanese local army commander, told an AFP reporter who visited the region with Sudan's Oil Minister Awad Ahmad al-Jaz.

A large contingent of Misseriya nomads from the paramilitary Popular Defence Force (PDF), a key battle force for the Sudanese military, patrolled the Heglig area with rifles and motorcycles, but without uniforms.

"We will fight for this border even without the government's permission, to protect our land," said Ismail Hamdien, a Misseriya leader who travelled to the battle scene to assess the situation.

Rebel forces that both Juba and Khartoum accuse are backed by the other were also reported to have joined in the fighting, and AU Commission chief Jean Ping called for a "halting of any support to rebel forces."

Oil operations in Heglig are run by the Greater Nile Petroleum Operating Company (GNPOC), a consortium led by China's state oil giant CNPC.

"There is serious concern among us," one Chinese oil worker said. "How can we work in this situation? We want the government to protect us because we are working for the people of Sudan."

Southern soldiers were on high alert along the border fearing fresh attacks after pulling out of Heglig, said Southern army spokesman Philip Aguer.

"It is not our policy to attack and occupy, but only to defend ourselves against unwarranted aggression," said Aguer, adding there had been no ground fighting Wednesday.

"We are monitoring the movement of large SAF (Sudan's army) convoys near the border ... our forces are ready to respond," he added.

More than two million people died in Sudan's 1983-2005 civil war between Khartoum and southern rebels before a peace agreement which led to South Sudan's independence.

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