Hu Jintao wants an immediate investigation into the killing

The president's extremely rare intervention follows an outcry over the beating to death of Lan Chengzhang outside the mine, in Shanxi province.

The mine owner is among several people who have been detained over the attack.

Some local officials suggested Mr Lan was not an accredited journalist and may have been trying to extort money.

President Hu and other senior members of the Communist Party are "demanding that the case be rapidly investigated and the results be reported as quickly as possible," the China News Service reported.

Dangerous mines

Lan Chengzhang died after being set upon by a gang as he investigated an illegal mine in Shanxi's Huiyuan county earlier this month. His colleague was injured.

China's mines are among the most dangerous in the world

Local officials reportedly described Mr Lan at the time as a "false journalist", and suggested he had been seeking payments in return for not reporting problems at the mine.

His newspaper, the Beijing-based China Trade News, said he had only just started with them and had not yet completed his trial period.

The owner of the unlicensed mine, who is suspected of ordering the attack, is one of seven people arrested over the killing. Three others are also being sought, state media reported.

The incident has caused a storm of protest from journalists and media groups both in China and abroad.

They have called for greater protection for reporters in a country where the media is strictly controlled.

China's coal mines are among the most dangerous in the world, with more than 5,000 deaths reported annually.

Mine owners are accused of frequently ignoring government regulations in search of greater profits.