The 29 Chinese workers captured by rebels more than a week ago in southern Sudan should be released soon, a spokesman for the insurgents said on Monday.

"We believe this will be very soon," Arnu Ngutulu Lodi of the Sudan People's Liberation Movement-North (SPLM-N) told AFP from Kenya. "It's not going to take long."

He said the rebels are in communication with the Chinese government, though not through a six-member mission sent by Beijing to Khartoum to help secure the release of the captives, who were involved in a road-building project.

They have been held since January 28 when SPLM-N destroyed a Sudanese military convoy between Rashad town and Al-Abbasiya and took over the area, the rebels said.

Lodi said the Chinese -- whom the Sudanese military refers to as hostages -- are safe.

According to China's official news agency Xinhua, the workers were taken after a rebel attack on their camp.

SPLM-N chairman Malik Agar last week discussed the workers' case with a Chinese diplomat and asked China to use its influence with Khartoum to help badly needed aid reach the country's war zone, Lodi said.

Agar held the talks in the Ethiopian capital Addis Ababa with Beijing's ambassador there.

China is Sudan's major trading partner, the largest buyer of Sudanese oil and a key military supplier to the regime in Khartoum.

Sudan has severely restricted the work of foreign relief agencies in South Kordofan and nearby Blue Nile state, where fighting began months ago between the government and ethnic minority insurgents who fought alongside the former rebels now ruling South Sudan.

The South gained independence from Khartoum last July after decades of civil war.

About 30,000 people fled when the rebels took control of villages in the Al-Abbasiya area on January 28, the United Nations said.

The UN has backed statements by the United States that there could be a famine unless urgent aid is allowed to enter South Kordofan and Blue Nile.

Lodi said Sudanese air force bombing killed two civilians in the village of Mandi, about 80 kilometres (50 miles) southeast of the state capital Kadugli, on Sunday night.

The Chinese captives are not near that area, he said.

Sudan's army spokesman denied bombing Mandi, saying: "We would never target civilians."

US President Barack Obama's spokesman last week condemned the "unjustified and unacceptable" bombing of civilians by the Sudanese military in South Kordofan and Blue Nile.