Sudanese rebels on Monday declared North Kordofan state a target in a widening offensive, as parliament met to discuss weekend attacks on the region which had been largely free from unrest.

Except for occasional rebel forays over the border from the conflict-plagued Darfur region, North Kordofan had been generally peaceful.

But on Saturday a rebel coalition struck a major North Kordofan town which residents said had been left unguarded and was hit during coordinated attacks in the insurgents' most audacious act in years.

"North Kordofan state has all become our target," Arnu Ngutulu Lodi, spokesman for the Sudan People's Liberation Movement-North (SPLM-N), told AFP.

SPLM-N, which has been fighting for two years in South Kordofan state, belongs to the Sudan Revolutionary Front (SRF) which also includes major insurgent groups from Darfur.

Lodi said that insurgents on Sunday shelled the airport area of Kadugli, the capital of South Kordofan, for the second time in two days.

He warned civil aviation to avoid the area, as well as the airspace in North Kordofan.

"It is becoming a target for us," Lodi said. "This is a very serious kind of warning. This whole area has become an operational area."

SRF said it attacked Umm Rawaba, the second-largest town in North Kordofan, and several other areas in North and South Kordofan as part of its strategy to reach the capital Khartoum and overthrow the 24-year regime of President Omar al-Bashir.

Parliament met in closed session to discuss the attacks while Defence Minister Abdelrahim Mohammed Hussein inspected damage from the weekend assault.

Speaking to troops in a state television broadcast, he said he wanted the area down to the South Sudanese border "cleansed of rebels".

The SPLM-N has shelled Kadugli periodically since late last year, but on Saturday for the first time targeted the airport region.

That barrage killed four soldiers, Lodi claimed, but residents reported only a few injuries.

They said they could not confirm that a second barrage occurred on Sunday, and reported the town as calm on Monday.

The government blamed rebels for killing civilians in its previous shellings of Kadugli, while rights groups have accused the Khartoum regime of indiscriminate aerial bombing elsewhere in the state.

A rebel statement said the Kadugli airport has become "a centre of control and command of National Congress Party forces and militias for directing its air and ground attacks against innocent citizens, therefore it becomes the direct target for the Sudanese Revolutionary Front forces."

Residents of Umm Rawaba, about 300 kilometres (190 miles) from Kadugli, complained their town had been left undefended when SRF briefly occupied it on Saturday.

The death toll was unclear but included some policemen, according to residents and officials.

A source in Sudan's Humanitarian Aid Commission said "there are huge numbers of displaced from different areas that were attacked," and officials are assessing the situation.

Villagers from Abu Kershola, one of the affected communities, told AFP they were living rough under trees and with little food after fleeing on Saturday.

Umm Rawaba, with a population of several thousand, is about 100 kilometres east of El Obeid, the capital of North Kordofan which produces gum arabica, an ingredient in soft drinks and other products. Sudan is the world's biggest producer of gum arabica.

In 2008 Darfur's Justice and Equality Movement rebels (JEM), who now belong to SRF, pushed all the way to Khartoum's twin city of Omdurman where government forces said they were beaten.

The attack in North Kordofan comes as the government, beset by internal political struggles, seeks a broad political dialogue with its opponents.

Last week Khartoum and the SPLM-N held their first direct talks in almost two years, but both sides said negotiations stalled.