The information minister for South Sudan's Unity state, Gideon Gatpan, said the oil-rich region was under attack by forces from Sudan for the second straight day on Tuesday.

"We believe the airstrikes were targeting the oil fields," he said, adding that there had been no casualties or damage reported.

South Sudan's President Salva Kiir claimed that Sudanese aircraft and ground troops attacked multiple positions in border regions the day before. Sudan's army confirmed that clashes took place but said South Sudanese forces struck first.

The fighting prompted Sudanese President Omar al-Bashir to suspect plans for talks with his southern counterpart aimed at resolving the countries' bitter disputes over oil and border regions.

On Tuesday, UN Secretary General Ban Ki-moon called on the two sides to come to a peaceful resolution.

Ban's spokesman said Sudan and South Sudan should "utilize to the fullest extent existing political and security mechanisms to peacefully address their differences."

The US, meanwhile, said it was "greatly alarmed" by the border fighting.

South Sudan split from Sudan in July, taking with it most of the country's known oil reserves.

mz/ng (AFP, Reuters)