Police say man was visiting North Sentinel Island, whose inhabitants are known to attack outsiders

Members of an isolated Indian tribe armed with bows and arrows have killed an American who encroached on their remote island, police said.

John Allen Chau, 26, is believed to have paid fishermen to ferry him to North Sentinel Island, home to a 30,000-year-old tribe known to aggressively repel outsiders.

“The fishermen in the dinghies tried to warn him it’s a risky thing,” said Denis Giles, an activist for the rights of tribal groups and a journalist on the Andaman and Nicobar Islands, the Indian territory where the incident took place.

He said Chau, who some Christian groups have claimed was a missionary, had been trying to find ways to reach North Sentinel Island and finally succeeded on Saturday, taking a dinghy with the fishermen, then completing the rest of the journey by kayak.

“Somehow he made it,” said Giles. He added: “The fishermen who were back in the dinghy saw an arrow hit him. Later they said he was taken deeper [into the island] and buried.”

The Andaman and Nicobar Islands are scattered across the juncture of the Bay of Bengal and Andaman Sea. They were colonised by the UK in the 1850s and used as a penal colony, including for Indian dissidents and freedom fighters involved in the 1857 uprising against British rule.

Anthropologists have evidence human life existed on the Andamans at least 2,000 years ago, while genome studies suggest the four native tribes on the islands – of which the Sentinelese are the most isolated – are at least 30,000 years old.

North Sentinel Island is about 20 sq miles and the Sentinelese are estimated to number about 100 people. They are thought to have had no contact with surrounding communities since 1991. Starting in the 1960s, anthropologists – protected by armed guards – succeeded first in exchanging gifts, then conducting field visits with the tribe, but abandoned their efforts around 25 years ago.

The Sentinelese people violently resist contact with outsiders. In 2006, two Indian fishermen who moored their boat to sleep were killed when the vessel broke loose and drifted on to the shore, according to Survival International, a tribal rights advocacy group. The tribe fired a volley of arrows at a helicopter sent to retrieve the men’s bodies.

TM Pandit, an anthropologist who had led efforts to contact the tribe, recalled his first contact with the tribe in an interview in September. “The tribespeople were on the beach, watching the boat come to the island,” he said.

“There was a large number of them. But there was no reaction or resentment from them. We went about a kilometre inside the forest.

“They did not come face to face with us, but rather hid in the forest, watching us. After some time, we came upon a large area of forest cleared for a camp. There were 18 small huts, with little fires burning in front of each, fenced off with sticks.”

Indian police said a murder case had been registered against “unknown tribesmen” and seven people arrested for helping Chau reach the island.

On Wednesday night Chau’s family posted on his Instagram page saying that they forgave his killers and asked that those who helped him be released. The family described him as a “beloved son, brother and uncle” as well as a Christian missionary. “He loved God, life, helping those in need and had nothing but love for the Sentinelese people,” the family said. “We forgive those reportedly responsible for his death.”

Chau had visited the Andaman and Nicobar Islands in the past and told locals he had a strong desire to visit the Sentinelese and preach to them, a police source told Reuters.

Giles said there had been confusion in the territory over whether the island could legally be visited since April, when the Indian government lifted some restrictions on tourists. “One among the islands which was opened up was North Sentinel island,” he said.

But Indian officials say there has been no change in the island’s status.

Sophie Grig, a senior researcher with Survival International, said that by trying to reach the island Chau had risked both his own safety and that of the tribe.

“This is one of the most vulnerable tribes on the planet,” Grig said. “He could be passing on diseases that could literally wipe them all out.”

Facebook Twitter Pinterest Tribespeople on North Sentinel Island, where Chau died. Photograph: Dinodia Photos/Alamy Stock Photo

The Indian government has what it calls a “hands off, eyes on” policy to the tribe, meaning officials moor boats near the island every few months to check on the inhabitants’ welfare.

The US consulate in Chennai, the capital of southern Tamil Nadu state, said it was aware of the reports of Chau’s death but spokeswoman Kathleen Hosie declined to comment further due to privacy considerations.

Shiv Visvanathan, a social scientist and a professor at Jindal Global Law School, said the North Sentinel Island was a protected area and not open to tourists. “The exact population of the tribe is not known, but it is declining. The government has to protect them,” he said.

Poachers are known to fish illegally in the waters around the island, catching turtles and diving for lobsters and sea cucumbers.

Only about 700 people belonging to the four native tribes of the islands are thought to remain, down from the 5,000 the British estimated were there when they arrived. They hunt wild animals and gather fruit, honey and insects.

• This article was amended on 23 November 2018 to correct John Allen Chau’s age