Rebels in Sudan's oil-producing border state of South Kordofan said on Sunday they were holding Chinese workers for their own safety after a battle with the Sudanese army.

The army has been fighting rebels of the SPLM-N in South Kordofan bordering newly independent South Sudan since June. Fighting spread to the northern Blue Nile state in September.

We are holding 29 Chinese workers after a battle with the army yesterday, a spokesman for the SPLM-N said. They are in good health. We are holding them for their own safety because the army was trying to strike again.

The army said rebels had attacked the compound of a Chinese construction company operating in the area between the towns of Abbasiya and Rashad in the north of the state and captured 70 civilians.

Most of them are Chinese. They (the rebels) are targeting civilians, said army spokesman Sawarmi Khalid Saad.

He said there had been no battle in the area and the army was now trying to rescue the civilians.

China's foreign ministry urged Sudan to guarantee the safety of Chinese personnel during the search and rescue process, according to a statement released in Beijing.

South Kordofan is the main oil-producing state in Sudan, while Blue Nile is rich in minerals such as chrome.

The fighting in both states has forced about 417,000 people to flee their homes, more than 80,000 of them to South Sudan, according to the United Nations.

Both states contain large groups who sided with the south in a decades-long civil war, and who say they continue to face persecution inside Sudan since South Sudan seceded in July.

The SPLM is now the ruling party in the independent south and denies supporting SPLM-North rebels across the border.

Events in South Kordofan and Blue Nile are difficult to verify because aid groups and diplomats are banned from areas where fighting takes place.

SPLM-North is one of a number of rebel movements in underdeveloped border areas who say they are fighting to overthrow Sudanese President Omar Hassan al-Bashir and end what they see as the dominance of the Khartoum political elite.

Sudan and South Sudan, which still have to resolve a range of issues including the sharing of oil revenues, regularly trade accusations of supporting insurgencies on each other's territory.

(Reporting by Ulf Laessing and Khalid Abdelaziz; additional reporting by David Stanway in Beijing)