A Thai court on Wednesday threw out defamation charges against a news agency for alleging environmental damage by a gold mine, a lawyer said, in a rare win for press freedom in the country.

Criminal defamation is a go-to weapon for powerful business and political players in Thailand, where activists, journalists and online critics are routinely swept up in court cases that often end in jail time.

The gold mine in northeastern Loei province has been the centre of a decade-long struggle between its Thai operator, Tungkum Ltd., and grassroots activists who say the mine has polluted the environment and harmed their health.

The company has filed more than a dozen lawsuits, including a criminal defamation case against state-funded broadcaster Thai PBS over a news clip produced by a 15-year-old girl who lives near the mine.

In the segment, which was part of the network's citizen journalist series, the teenaged narrator said six villages had been "environmentally affected by the gold mining industry".

The mining firm hit back by charging Thai PBS and four of its staff with criminal defamation.

It also demanded 50 million baht ($1.4 million) in compensation and a five-year suspension of the station's operating licence, according to rights groups.

But the case was dropped Wednesday by a Bangkok court, said Thai PBS's lawyer Saengchai Rattanasereewong.

Judges decided to exonerate the network because it reported "comments based on good faith", he said in an interview aired on Thai PBS.

"Media who have a duty to report such comments are also (protected under the law)," he added.

Watchdog Fortify Rights welcomed the ruling, hailing it as a crucial step towards protecting press freedoms in the junta-run country.

"However, there's still a long way to go when it comes to ensuring fundamental freedoms in Thailand," the group's director Amy Smith told AFP.

Earlier this month a prominent British migrant rights activist, Andy Hall, left Thailand after more than a decade under pressure from a mounting pile of lawsuits over his efforts to expose labour abuses in the fishing and poultry industries.

The space for free expression has also narrowed significantly since Thailand's military grabbed power in a 2014 coup.

The junta has banned political gatherings, detained its critics for "attitude adjustment" sessions and intimidated the press.