Rebels in Sudan's Blue Nile state said on Monday they had destroyed a Sudanese tank and captured two others but the army dismissed the report as propaganda while acknowledging fighting in another border region.

Both sides said they had fought in South Kordofan state despite a Khartoum-Juba deal aimed at cutting South Sudanese support for the insurgency.

The ethnic and religious-minority Sudan People's Liberation Movement-North (SPLM-N) said it captured the tanks and other weapons during a three-day battle that ended Sunday with their seizure of Surkum, 50 kilometres (30 miles) northwest of Kurmuk town in Blue Nile.

The village was a military outpost from which government forces planned to launch attacks, SPLM-N spokesman Arnu Ngutulu Lodi told AFP.

Sudanese army spokesman Sawarmi Khaled Saad denied the incident. "They didn't attack any of our positions in Blue Nile. They only want fabrication and media propaganda," he told AFP.

The army and rebels both said there had been fighting around Kologi town in the eastern part of oil-producing South Kordofan, where the SPLM-N has been fighting since June last year. Fighting spread to Blue Nile in September 2011.

Hundreds of thousands of people have been displaced or severely affected by the violence in both states, the United Nations says.

"Yesterday they tried to attack one of our positions near Kologi and we responded, killing 15 of them," Saad said.

The rebels' Lodi said insurgent forces attacked and then withdrew, but remain in the area.

Both sides at times have an interest in inflating casualty figures, a Sudan analyst says.

Last week, the rebels launched an unprecedented artillery barrage on the South Kordofan state capital Kadugli, which official media said killed seven women and children.

The United Nations condemned the attack.

SPLM-N said it regretted any civilian casualties that may have been caused but said its artillery fire was self-defence in the face of government shelling and aerial bombardment of rebel positions.

The action came after Sudan and South Sudan in late September signed deals on security and cooperation that they hailed as ending their countries' conflict.

The neighbours fought along their undemarcated frontier in March and April, sparking fears of wider war and leading to a UN Security Council resolution ordering a ceasefire and the settlement of unresolved issues, under African Union mediation.

Among the deals reached in Addis Ababa is agreement on a demilitarised border buffer zone designed to cut support for SPLM-N rebels in South Kordofan and Blue Nile states.

Khartoum accuses the government in Juba of backing those insurgents, and South Sudan in turn says Sudan has armed rebels in its territory.

The SPLM-N battled alongside insurgents from southern Sudan who waged a 22-year civil war which ended in a 2005 peace deal leading to South Sudan's independence last July.

The UN has stressed the need for a political settlement in South Kordofan and Blue Nile.