Darfur rebel group the Justice and Equality Movement (JEM) said on Monday that it carried out a deadly attack on Sudanese army positions in South Kordofan alongside anti-government forces there.

It is the first time the JEM, Darfur's most heavily armed rebel group, has claimed to fight alongside the southern-aligned militia (SPLA north) in Sudan's ethnically divided border state, since fighting first erupted there on June 5.

The alleged joint attack took place just two weeks after Malik Agar, who heads the political wing of the ex-rebel forces (SPLM north), warned of a "coordinated" uprising between Blue Nile state in the east and Darfur in the west, unless Khartoum agreed to a ceasefire in South Kordofan.

"Today, in a joint operation between JEM troops and the SPLA north, we attacked SAF (Sudanese Armed Forces) camps in Pisea, 25 kilometres (16 miles) south of Kadugli," one of the JEM's top leaders, Al-Tahir al-Fatih, told AFP.

"We took control of the camps and the army withdrew," he said, adding that the rebels killed more than 100 soldiers and captured numerous weapons but lost only one man, despite coming under fire from Antonov bombers and army helicopters.

The army spokesman was not immediately available to respond to the rebel claims, which could not be independently verified.

For six weeks, heavy fighting has raged across South Kordofan, between the army and Nuba militiamen who fought with SPLA, the ex-rebel army of the south, during their decades-long conflict with Khartoum.

South Sudan proclaimed formal independence from the north on July 9, and observers say opposition from north Sudan's neglected peripheral regions like Darfur and South Kordofan may grow in the wake of southern secession.

An internal UN report seen by AFP said the army's systematic attacks, targeting the state's indigenous Nuba peoples, could amount to war crimes and crimes against humanity, charges strongly denied by the government, which says it is fighting an internal rebellion.

On Sunday, JEM raised the possibility a fresh attack on the Sudanese capital.

"Those who carried out the heroic attack on Omdurman and terrorised the regime of (President Omar) al-Bashir are capable of repeating the same attack with their partners in the struggle," the group warned in a statement.

In May 2008, JEM fighters launched an unprecedented march on Khartoum, reaching the capital's twin city of Omdurman just across the Nile from the presidential palace before being repulsed with heavy losses.