Khartoum has restricted access for aid workers and the UN in violence-infested southern states [Reuters]

At least 29 Chinese workers have been released, according to Sudan's foreign ministry, 10 days after they were kidnapped in the oil-producing state of South Kordofan, bordering newly independent South Sudan.

The Chinese workers were flown out from Kauda in South Kordofan by the International Committee of the Red Cross (ICRC), the campaign group and Sudan's foreign ministry said on Tuesday.

"The Sudanese foreign ministry affirms to the government and people of China that Sudan's government seeks to protect Chinese investments and workers involved in it," the ministry said in a statement.

The workers later arrived in Kenyan capital, Nairobi, "safe and sound", China's official Xinhua news agency said, citing a statement from the Chinese foreign ministry.

A spokesman for the South Sudan People’s Liberation Army (SPLM-North) spokesman, Arnu Ngutulu Lodi, declined to comment

The incident has been an embarrassment for the Sudanese government, which is trying to boost investment from China, its main political and trade ally, as it seeks to overcome a severe economic crisis.

China is an ally of both north and south and the main buyer of South Sudanese oil as well the biggest investor in Sudan.

Humanitarian crisis

The SPLM-North says it had taken the construction workers for their own security after a battle with the Sudanese army in South Kordofan.

Incidentally, SPLM-North leaders met Chinese officials in Ethiopia last week.

The Sudan government has been battling the group in South Kordofan and another Sudanese border state, Blue Nile, which has led to a humanitarian crisis with almost 417,000 civilians having fled for safety.

Both South Kordofan and Blue Nile are home to large communities who sided with the South during decades of civil war with Khartoum.

Khartoum has restricted access for aid workers and the UN in both the states.

Many say they have been marginalised by the Khartoum government since South Sudan declared independence in July under a 2005 peace deal.

North has accused the SPLM, the ruling party in South Sudan, for backing SPLM-North, a charge the South has dismissed.

The kidnap was the third abduction of Chinese people in Sudan since 2004 and highlighted the risks to China's expansion in Africa in search of minerals and energy.