Indonesian authorities has ordered a giant US-owned gold and copper mine to suspend operations until an investigation into a fatal tunnel collapse is completed.

Freeport-McMoRan shut down all operational activities at the Grasberg mine in Indonesia’s easternmost Papua province for two weeks following the accident when a tunnel at the underground facility caved in, leaving 28 workers dead.

But some open-pit mining and milling operations were resumed last Tuesday, prompting thousands of workers to protest, saying they refuse to return to work while a probe is underway.

Indonesia’s energy and resources ministry ordered Freeport to ground operations to a halt while investigations are ongoing, reports AFP.

“All operations at the mine should stop until the team makes safety recommendations,” chief mine inspector Syawaluddin Lubis told AFP, adding that they could only carry out administrative and maintenance work.

The stoppage could last two months, the ministry said, and could take even longer if the investigation proved to be complex. Freeport has also said it will conduct its own probe and will assess the impact of halted operations to stockpiles.