Twenty-nine Chinese workers described as hostages by Sudan's military are in good shape and will be released when the security situation allows, their rebel captors told AFP on Monday.

"They are okay. They are doing well," said Arnu Ngutulu Lodi, spokesman for the Sudan People's Liberation Movement-North (SPLM-N) in South Kordofan state.

He dismissed an official Sudanese media report which quoted state governor Ahmad Harun as saying security forces "have liberated 14 of the Chinese workers who were kidnapped by the rebels".

"Ahmad Harun is lying," Lodi said.

Beijing's official news agency said the rebels still hold 29 Chinese workers while 17 others were moved to safety by the Sudanese army when rebels attacked the workers' camp on Saturday.

Chinese ambassador to Sudan Luo Xiaoguang and a number of Sudanese officials received the returning Chinese workers upon arrival at Khartoum airport, the Xinhua news agency said.

Luo expressed appreciation for the Sudanese government's efforts to help the Chinese workers and urged Khartoum to continue and intensify the search for those missing.

"This incident is individual and does not affect the bilateral ties between Sudan and China," the ambassador said, describing relations as "strong."

Another group of 12 Chinese, working for the same company which is constructing a road in South Kordofan, is expected to arrive later in the day, Xinhua said.

"They are held hostage by SPLM," said the Sudanese army spokesman Sawarmi Khaled Saad, who added soldiers were searching for the captives, "and SPLM are responsible for their safety".

Lodi denied there was an attack against the Chinese.

"The SPLM is fighting the government troops," he said, and the Chinese came into rebel custody when SPLM-N forces took control of the area after destroying a Sudanese military convoy between Rashad town and Al-Abbasiya in the northeast of the state, which has been at war since June.

Lodi said nine members of the Sudan Armed Forces (SAF) were also captured.

Release of the Chinese depends "of course" on the security situation, the rebel spokesman said from Kenya.

"We will inform them at the right time," he added. "We are very concerned about their security and safety."

China's commerce ministry urged companies and personnel operating in Sudan to strengthen security after the incident.

"The commerce ministry reminds relevant companies and personnel to pay close attention to changes in the local security situation, strengthen their own security and ensure the safety of people and property," it said in a statement.

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

There is growing international concern over the situation in South Kordofan and nearby Blue Nile, another southern border state, where a similar conflict broke out in September.

The government is fighting 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.

Food shortages would become critical by March without substantial aid deliveries into South Kordofan and Blue Nile, the US ambassador to the United Nations, Susan Rice, has said.

Khartoum has severely restricted the work of foreign relief agencies in the war zones.

It cited security concerns and also accused aid workers of using United Nations flights to deliver arms and ammunition to the rebels -- a claim for which the UN's top humanitarian official said there was "no evidence".

Princeton Lyman, the US administration's special envoy for Sudan, told reporters last week the situation is so dire Washington has warned Khartoum it would consider ways for aid to be sent in without Sudanese government approval.