A Canadian and an Iraqi were seized from the field run by a consortium of Sudanese, Chinese, Indian and Malaysian partners, he said.

A Chinese foreign ministry spokesman said no citizens of his country were injured in the reported attack, but also urged Sudan to step up safeguards.

"We're taking the reports very seriously and hope the parties involved will immediately cease fire and solve the Darfur issue through peaceful negotiations," Liu Jianchao, Chinese foreign ministry spokesman, said.

"We also hope that Sudan will take China's concerns seriously and adopt measures to ensure the safety of Chinese personnel."

Critics say China's military aid and oil investment in Sudan fuelled the north-south war and the more recently the separate conflict in the western region of Darfur.

International experts say about 200,000 people have died and 2.5 million fled their homes in Darfur since 2003 when rebels took up arms against the government.

The conflict escalated when it mobilised militias to crush the revolt against the government. Sudan has understated the number of casualties saying only 9,000 have died.