The Indonesian Navy has disclosed that one of its marines, Sgt Major Alfriansyah, had been apparently abducted by a group of Thai fishermen.
The man was reportedly abducted after he had witnessed a group of fishermen fishing in Bintan waters, which is Indonesian territory.
"Alfriansyah and a local fisherman approached the Thai fishermen's boat to collect evidence. But neither returned," First Admiral Agus Heriyana said last week.
A team of investigators was in pursuit of the boat, he said.
The incident happened last Tuesday but the locals only reported it to naval authorities a day later.