Sudanese rebels said they attacked government forces in North Kordofan on Wednesday, days before a Khartoum deadline to halt South Sudan's oil exports over allegations it is backing the insurgents.

The Justice and Equality Movement, a Darfur-based group which is part of a wider rebel alliance, said it attacked a military convoy at Sidrah, about 30 kilometres (20 miles) south of El Rahad town.

"Fighting is still going on," JEM spokesman Gibril Adam Bilal told AFP.

Sudan's army spokesman could not immediately be reached.

The JEM and the various factions of the Sudan Liberation Army in Darfur belong to the Sudan Revolutionary Front (SRF), an alliance with insurgents fighting in South Kordofan state south of Sidrah, and in Blue Nile.

The SRF staged its first joint operation in April, sweeping through a previously peaceful part of North Kordofan near Sidrah as part of coordinated attacks in the region.

Analysts said those rebel strikes humiliated the authorities, who took a month to retake one of the seized areas, Abu Kershola.

In June, Khartoum gave oil companies until August 7 to stop transporting crude from South Sudan through a Sudanese export pipeline after President Omar al-Bashir accused the Juba government of backing the rebels in the north.

Juba denies supporting the insurgents and in turn says Khartoum assists rebels on southern soil.

Observers say in reality both governments have aided each other's rebels.