Clashes have broken out between the armed forces of Sudan and South Sudan in several disputed border regions, both sides said.

Sudan's army spokesperson Sawarmi Khalid Saad confirmed the fighting in the border area of Sudan's South Kordofan state and the southern Unity state, without giving the exact locations. He did not say who had started the fighting.

"I think due to this attack, the government now is changing its strategy to deal with the southern government," Rabie Abdul Atti, an advisor to Sudan's minister of information, told Al Jazeera.

The fighting has forced President Omar Hassan al-Bashir to suspend plans to visit South Sudan on April 3, Sudan's state radio reported.

In a brief text message, the broadcaster said the suspension came after an attack on the oil-producing area of Heglig, parts of which are claimed by both Sudan and South Sudan.

Bashir had been due to hold talks with his southern counterpart Salva Kiir during his visit to the southern capital Juba to resolve tensions that have surged since South Sudan seceded from Sudan last year.

UN leader Ban Ki-moon has called for an end to the border clashes.

"The secretary general is deeply concerned about the military clashes in the border region and calls on the governments of Sudan and South Sudan to fully respect and implement the agreements they have already reached on security, border monitoring and Abyei," said UN spokesman Martin Nesirky.

The two Sudans fought a two-decade civil war up to 2005 in which two million people died. Since their separation the two sides have been in dispute over oil reserves, their frontier and the disputed territory of Abyei.

PHOTO CAPTION

A map of Sudan and South Sudan

Al-Jazeera