BEIJING (Reuters) - China has unveiled new rules telling officials not to cover up what should be publicly available information using the excuse it is a state secret, in what state media said was a move towards greater government transparency.

China has notoriously vague state secret laws, covering everything from the number of people executed every year to industry databases and even pollution figures, and information can be retroactively labeled a state secret.

The issue received international attention in 2009 when an Australian citizen and three Chinese colleagues working for mining giant Rio Tinto were detained for stealing state secrets during the course of tense iron ore negotiations.

But the government has come under pressure from its own people to be more open, especially on sensitive issues like the environment, which have no obvious implications for national security.

The new rules, carried by the official Xinhua news agency late on Sunday, mandate that government departments "must not define as a state secret information which by law ought to be public".

Xinhua said that the move, due to come into force on March 1, was "an effort to boost government transparency".

However, in keeping with the vague nature of state secrecy laws, the rules offer no explanation for what public information will be covered that cannot be called a state secret.

The rules also state that "the scope of what is secret should be adjusted in a timely manner according to changes in the situation".

Officials who discover that state secrets have been compromised will have to report the problem within 24 hours and will be punished if they cover up the leak or fail to report it, Xinhua said.

Chinese officials, particularly at the local level, often seek to invoke secrecy laws to prevent embarrassing problems that could lead to punishment, such as police brutality or pollution, from being reported to more senior officials.

(Reporting by Ben Blanchard; Editing by Ron Popeski)