Sudanese war planes have launched renewed air strikes against South Sudan, violating a UN Security Council resolution to end weeks of a bitter border conflict, the South's army said Wednesday.

"The Republic of Sudan has been randomly bombarding civilian areas," said Southern army spokesman Kella Kueth, who claimed the air strikes hit the border states of Upper Nile, Unity and Western Bahr el-Ghazal on Monday and Tuesday.

It was not possible to independently confirm the reports and Sudan has repeatedly denied it has bombed the South.

"The people of Khartoum, they just deny," Kueth said, adding that both fighter jets and Antonov airplanes carried out the air raids.

Both sides say they are complying with a United Nations Security Council resolution which ordered them to stop fighting from last Friday, amid international concern that the rivals could return to all out war.

Border clashes with South Sudan began in late March, escalating with waves of Sudanese air strikes against South Sudanese territory and the South's 10-day seizure of the Heglig oil field from Khartoum's army.

The South's army confirmed it had pulled back 10 kilometres (six miles) south of the contested border line, in accordance with the UN deadline Wednesday to do so. However the border is undemarcated.

"Yes, we have done so... but we are focusing on the bombing," Kueth added.

The UN resolution threatens additional non-military sanctions if either side fails to meet its conditions, including ordering Sudan to halt air strikes.

It also lays down a May 16 deadline for Khartoum and Juba to "unconditionally resume negotiations" mediated by the African Union.

Troops from the rival armies are dug into fortified defensive positions along the restive border.

The reported attacks come as UN High Commissioner for Human Rights Navi Pillay visits South Sudan to discuss the protection of civilians affected by the border fighting.

Sudan has accused the South's army of occupying border areas Khartoum claims as theirs, in the frontier zone between Sudan's South Darfur state, and the South's Western and Northern Bahr el-Ghazal states.

However, the South reject those claims, saying clashes there were between Khartoum's army and northern rebels.

"We, the South, do not have anything to do with Darfur, we do not concern ourselves about that," Kueth said.

Sudan also accuses the South of backing rebels from Darfur as well as those fighting in Sudan's South Kordofan state and Blue Nile.

Juba rejects the claims, and in turn accuses Khartoum of backing rebels on its territory, a tactic it used to deadly effect during their 1983-2005 civil war.

The South also accuses Khartoum of occupying several parts of its territory, including the Lebanon-sized Abyei region, claimed by both sides but which Sudan's army stormed last year forcing over 100,000 people to flee southwards.

South Sudan broke away from Sudan in July after a 2005 peace deal ended one of Africa's longest civil wars, which killed about two million people.

But tensions soon flared again over a series of unresolved issues, including the border, the future of disputed territories and oil.

As a result of independence, landlocked South Sudan took with it about 75 percent of the formerly united Sudan's oil production, worth billions of dollars.

In a key dispute, the two sides are unable to agree on how much the South should pay to export its crude through a northern pipeline and port, leading the Juba government in January to shut its production after Khartoum began seizing the oil in lieu of payment.