Jakarta – An Indonesian court ordered mining giant PT Freeport Indonesia on Tuesday to improve its toxic waste management after it was found guilty of giving false information over a fatal accident at a mining site last year.

The South Jakarta court backed a suit from leading environmental group Walhi which accused the copper and gold miner of presenting a misleading report to parliament on a landslide at its mine in the remote eastern province of Irian Jaya. Four workers were killed during that landslide in May last year at the Wanagon Lake waste dump.

"The defendant did not reveal what actually occured during the incident. In parliament they gave information that was contradictory ... It was manipulative and misleading," presiding judge Rusmandani Ahmad told the court.

Freeport plans to appeal the ruling. Company officials were not immediately available for comment. Ahmad said Freeport – a unit of US-based Freeport McMoRan Copper & Gold Inc – told the parliamentary hearing the landslide did not result in loss of life and it was due to natural causes not negligence.

Walhi chief Emmy Hafild hailed the ruling as a victory but said it was also moderate. Walhi did not seek damages, only a public apology. "Yes, it's lenient. But it's still a landmark as Walhi has never won a case against these companies before," Hafild told Reuters.

The mine in jungle-clad Irian Jaya is one of the largest in the world and has been at the centre of controversy for years over its impact on the surrounding region.