Police in India have admitted it may not be possible to retrieve the body of Christian missionary John Allen Chau, a US citizen who travelled to a remote island and was killed by its tribespeople.

The 27-year-old is believed to have died on 17 November after repeatedly trying to make contact with hunter-gatherers living in isolation on the island of North Sentinel, in the Andaman and Nicobar Islands chain.

Fishermen say they saw members of the Sentinelese tribe dragging Mr Chau’s body and burying him on a beach, and have been working with the police to try to identify the precise location of his remains.

But officers have now made several attempts to travel to the island by boat, only to turn back when confronted by tribespeople armed with spears, bows and arrows.

Authorities have not given up hope of retrieving Mr Chau’s body but have concluded after extensive discussions with experts that it will not be possible as long as the Sentinelese resist.

“They are a treasure,” police chief Dependera Pathak said of the tribe. “We cannot go and force our way in. We don’t want to harm them.”

Mr Pathak said police were still exploring their options, including “what kind of friendly gesture we can make” to win over the trust of the tribespeople.

But Survival International, a human rights organisation campaigning on behalf of threatened and uncontacted tribes around the world, called on the Indian authorities to abandon their efforts.

“Any such attempt is incredibly dangerous, for the Indian officials but also for the Sentinelese, who face being wiped out if any outside diseases are introduced,” director Stephen Corry said.

“The risk of a deadly epidemic of flu, measles or other outside disease is very real, and increases with every such contact. Such efforts in similar cases in the past have ended with the Sentinelese attempting to defend their island by force.

“Mr Chau’s body should be left alone, as should the Sentinelese.”

Ending attempts to retrieve the remains may actually be in keeping with Mr Chau’s own last wishes. In his final journal entries and letters to his family, Mr Chau showed he was aware of the risks of attempting to convert the Sentinelese people to Christianity.

In one entry on 16 November, he describes kayaking to the island and encountering its people for the first time. A juvenile member of the tribe fired an arrow at him, he wrote, piercing his waterproof Bible and forcing him to retreat to the waiting boat.

Before heading back to the island that evening, he wrote in a letter to his family: “You guys might think I’m crazy in all this but I think it’s worth it to declare Jesus to these people.

“Please do not be angry at them or at God if I get killed… This is not a pointless thing – the eternal lives of this tribe is at hand [sic].”

And then, scrawled in the margins but clearly underlined for emphasis, the words: “Don’t retrieve my body.”

Police are now examining the only recent precedent for the case – an incident in 2006 when two Indian fishermen lost control of their vessel and accidentally washed up on North Sentinel.

Both men were killed by the tribespeople and buried on the beach. Witnesses said they were later dug up and the remains propped up on bamboo stilts, facing out to sea. Tribespeople resisted efforts to reach the island then and, ultimately, the bodies were never recovered.

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“We are looking carefully at what happened then, and what [the Sentinelese] did,” Mr Pathak said.

A murder case has been opened into Mr Chau’s death but the suspects – the islanders – are simply listed as “unknown persons”. Seven people, including five fishermen, have been charged with helping him reach the island.

The wishes of Mr Chau’s family are unclear, though in a statement they asked “for the release of those friends he had in the Andaman Islands” who assisted in his journey.

“He loved God, life, helped those in need, and had nothing but love for the Sentinelese people.

‘We forgive those reportedly responsible for his death,” the statement read.

It is unclear whether US authorities will push for the retrieval and eventual repatriation of Mr Chau’s body.

A State Department official told The Independent: "We are aware of reports concerning a US citizen in the Andaman & Nicobar Islands. The welfare and safety of U.S. citizens abroad is one of the highest priorities of the Department of State. When a US citizen is missing, we work closely with local authorities as they carry out their search efforts.