Fighting has intensified between troops and rebels in Sudan's South Kordofan region, adding to humanitarian needs in an area where more than one million people were already affected, the UN said on Thursday.

The fighting that began three years ago "has intensified in April-May," the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said in its weekly bulletin.

It said this followed the government's announcement that a "decisive" campaign against the rebel Sudan People's Liberation Movement - North (SPLM-N) would continue.

"The recent offensive by the Sudanese Armed Forces supported by the Rapid Support Force -- a government-affiliated paramilitary force -- on SPLM-N areas over the past few weeks has resulted in a number of civilian casualties and repeated massive civilian displacement", OCHA said.

Like the 11-year war in Sudan's western Darfur region, the fighting in South Kordofan and Blue Nile states has been fuelled by complaints among non-Arab groups of neglect and discrimination by the Arab-dominated regime.

African Union-led peace talks between the government and the rebels were suspended early this month, tentatively to resume later in May.

"The SPLM-N has reported that in total an estimated 90,000 people were displaced in South Kordofan over the past month," adding to about 800,000 who the rebels estimated were already displaced or severely affected in areas of South Kordofan and Blue Nile under their control, OCHA said.

The UN has no access to rebel zones and cannot verify such figures, "let alone reach affected people with assistance," OCHA said.

Almost 26,000 people have also recently fled from rebel zones into government-held areas, adding to 1.2 million there who were already affected by the war, OCHA said.

At a press conference in Khartoum on Wednesday General Abbas Abdelaziz, who heads the Rapid Support Forces (RSF), confirmed that his men are "fighting with SAF in South Kordofan."

He denied allegations that the RSF had abused civilians in Darfur.