China's Foreign Ministry is calling for the immediate release of 29 Chinese workers who remain in captivity after being abducted by rebels in southern Sudan on Saturday.

Foreign Ministry spokesperson Liu Weimin said Tuesday that his office has sent a government delegation to help secure the release of the abducted workers.

The construction workers were captured Saturday when rebels in Sudan's South Kordofan state attacked their camp.

China's official Xinhua news agency says 29 are still being held captive by the rebels, while another 18 have fled to safety.

Chinese officials said the Sudanese army has tracked down and moved 17 of the escaped workers to a safe location, but that one is still missing.

Many of those who fled began arriving Monday in the Sudanese capital, Khartoum.

The kidnappings have threatened to damage relations between Sudan and its powerful Chinese ally. China is the largest buyer of oil from Sudan.

But China's ambassador to Sudan, Lui Xiaoguang, said Monday that the kidnapping is an individual incident and will not affect ties between the two countries.

The spokesman for the rebel Sudan People's Liberation Movement-North said the workers were taken Saturday after a battle with Sudanese troops in South Kordofan state, and were only being held for their own protection.

South Kordofan borders newly independent South Sudan, which broke away in July. The SPLM-N is a branch of the rebels who fought for the South during Sudan's long north-south civil war. Fighting broke out last year between Sudan and rebels in South Kordofan and in another border state – Blue Nile.