Lan Chengzhang, who worked for the China Trade News, died of an apparent brain haemorrhage on January 10 after more than 20 thugs set upon him and his taxi driver at the mine in Hunyuan County, Datong City of the northern province of Shanxi.

"Three suspects have been caught and the police are trying their best to find the remaining ones," the Beijing News said, quoting an unnamed police officer in the city of Datong.

China's coal mines are the deadliest of any major producer, with a total of 4,746 workers killed in accidents in 2006, as collieries push production beyond safety limits to pursue soaring profits.

Many mines closed for breaching safety rules open again illegally.

Gu Shengming, spokesman for the Datong City government, which oversees Hunyuan, told Reuters today that those being sought included the mine owner.

"It is an illegal mine, but it was closed a long time ago by the villagers," Gu said by telephone. He declined to give details.

Officials in Shanxi, which produces a quarter of China's coal, have said Lan was not an accredited reporter and suggested that he might have been seeking payoffs in return for not reporting problems at the mine.

A Hunyuan propaganda official repeated that line to the Beijing News.

"There are fake reporters coming almost every day, demanding payoffs in exchange for positive press or by threatening negative stories," he said.

However, Lan's family members said Lan went to the mine holding an official letter of introduction from The Trade News.

The Trade News editor-in-chief has said Lan was "certainly a real reporter," Chinese media reported. Chinese newspapers said in commentaries this week that Lan's lack of official approval was no excuse for murder.

Gu, the Datong spokesman, declined to answer questions about Lan's identity.

"This is a criminal case being investigated by our best police officers. I believe we'll know what actually happened and how the beating started very soon," Gu said.