image copyrightGetty Imagesimage captionThe Sangihe gold mine is highly controversial

Indonesian police are looking into the sudden death of an official who fought against a controversial gold mine, following calls for an investigation.

Helmud Hontong, deputy regent of Indonesia's remote Sangihe islands, died during a flight last Wednesday.

Rights groups say his death falls into a pattern of violence against people threatened for standing up for environmental rights.

But police say an initial post mortem examination points to a natural death.

The 58-year old politician appeared in good health before his flight on Bali island, but 20 minutes into the journey began feeling dizzy, according to his aide travelling with him.

He then "lost consciousness and blood flowed from his mouth and nose" soon afterwards, Hermen Kontu told Reuters news agency.

He was declared dead on arrival at the Sultan Hasanuddin International Airport in Makassar city.

While authorities have said the suspected cause of death was a chronic illness and heart failure, police are carrying out additional investigations.

'The mine will destroy the island'

by Raja Eben Lumbanrau, BBC Indonesia

Helmud Hontong died two days after my BBC Indonesia report into the fight against the gold mine, was released and went viral on social media in Indonesia.

I travelled to the remote jungle-covered island, near the Philippines border, to see what would be lost if the gold mine went ahead. I trekked through the thick forest around Mount Sahendarum with ranger Anius Dadoali to catch a sight of the endangered Cerulean paradise flycatcher (Seriwang sangihe), a bird only found in the steep valleys of this island.

"If the mines come here, the birds will become extinct, the forests will be destroyed and then landslides will happen and people will die. I can't imagine what our lives will be like," said Anius Dadoali. He has spent decades trying to protect the forest and the birds from poachers and illegal logging.

Mount Sahendaruman is included in the 42,000 hectares mining permit granted to the Mas Sangihe Mining Company (TMS). The island itself is only 73,000 hectares.

image captionRanger Anius Dadoali has spent decades trying to protect the forest

Merah Johansyah from the Mining Advocacy Network (JATAM) fears the mining project has the potential to completely destroy the island.

"On a small island like Sangihe, everything is limited, fresh water is limited, the ecology is limited. If half the island becomes a mining area, it will sink the island," he told BBC Indonesia.

His group says there are 55 islands in the Indonesian archipelago that have been completely destroyed by mining.

Mr Hontong had been a vocal critic of a 42,000 hectare gold mine project on his island.

Mining firm PT Tambang Mas Sangihe had received the concession for the mine in January, but opponents of the project say it threatens the islands forests, birds and the water supply to the islanders.

On 28 April, Mr Hontong wrote to the responsible ministry urging authorities to revoke the permit over environmental concerns.

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Indonesia's human rights commission Komnas HAM said it had asked police to investigate the case after complaints from Sangihe islanders, mostly farmers and fishermen.

Amnesty International said the politician's death fell into a pattern of violence and threats against people fighting for environmental and land rights issues.

But Alfred Pontolondo, coordinator of the Save Sangihe Island environment group, said he didn't want to "speculate on his death".

"Let the police process it legally if there's any suspicion."