Senior leaders from Sudan and South Sudan will meet Thursday in the Ethiopian capital to avert all out war following days of airstrikes and bloody border violence, officials on both sides said.

Sudan's Undersecretary of Foreign Affairs Rahamatalla Mohamed Osman said he was in Addis Ababa "to represent my country in the negotiations... with regards to security along the border."

South Sudan official Pagan Amum said he would travel to Ethiopia for African Union-mediated talks to stop the bitter clashes escalating into war.

"What we expect to achieve is the cessation of hostilities," Amum said by telephone from the South Sudanese capital. "We will stop the fighting that is there, and ensure that this does not erupt into war between the two countries."

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 in contested oil-rich border regions, the worst since South Sudan declared independence from Khartoum last July after decades of civil war.

The meeting was scheduled to take place before fighting broke out Monday.

Osman said the mood remained tense, which could jeopardize further talks between the two countries.

"We are talking about security arrangements at a time when there are attacks," he told AFP. "I am not sure we can accept any more offers (from the South)," he added, warning the clashes could create a stalemate.

However, Amum urged both sides to "rescue the positive spirit" of earlier talks, and said he remained confident fighting will stop after the meeting.

The African Union and the UN Security Council 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 (six miles) either side of the border.