Chinese workers captured by Sudan South Kordofan rebels They are being held in the Nuba mountains "until further notice" because of the security situation. "Today is a little bit calm but we are expecting at any time SAF may launch an attack on us," he said. Spokesmen for the Sudanese army and the Chinese embassy could not be immediately reached for comment by AFP. But the embassy told China's official Xinhua news agency that more than 20 Chinese nationals were missing after a rebel attack on the camp of a Chinese company. Xinhua quoted an official as saying the embassy "has started implementation of the emergency mechanism to follow up the issue" and contact Sudanese authorities. China is a major military supplier to the regime in Khartoum, and the largest buyer of Sudanese oil. There is growing international concern over the situation in South Kordofan and nearby Blue Nile state, where a similar conflict broke out in September. The government is fighting ethnic minority insurgents once allied to the former rebels who now rule South Sudan. The South gained independence from Khartoum last July after decades of civil war. Food shortages would become critical without substantial aid deliveries into South Kordofan and Blue Nile by March, 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.