NEW DELHI -- A rights group that works to protect tribal people has urged Indian authorities to abandon efforts to recover the body of an American who was killed by inhabitants of an island where outsiders are effectively forbidden by Indian law. The group, Survival International, said the islanders could be exposed to deadly diseases if rescuers set foot on North Sentinel Island, where John Allen Chau was killed earlier this month.

Chau traveled to the island by paying fishermen to smuggle him. The fishermen told authorities they saw the Sentinelese bury Chau's body on the beach.

Notes that Chau left behind said he wanted to bring Christianity to the islanders. Indian officials have traveled repeatedly in recent days near the remote island but have not set foot on it.

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Scholars believe the Sentinelese are descendants of Africans who migrated to the area about 50,000 years ago and survive on the small, forested island by hunting, fishing and gathering wild plants. Almost nothing is known of their lives, except that they attack outsiders with spears or bows and arrows.

Survival International's director, Stephen Corry, said in a statement Monday that any efforts to recover the body would be "incredibly dangerous" for both Indian officials and the Sentinelese, who face being wiped out if any outside diseases are introduced. "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," Corry said.

He said the body of Chau "should be left alone as should be the Sentinelese." Indian anthropologist T N Pandit, who has made contact with the Sentinelese, expressed a similar view to BBC News.

Pandit said they shouldn't be labeled as hostile. "Sentinelese are a peace-loving people. They don't seek to attack people. They don't visit nearby areas and cause trouble. This is a rare incident," he told the BBC.

There has been no significant contact with the Sentinelese for generations. Anthropologists used to occasionally drop off gifts of coconuts and bananas, but even those visits were stopped years ago.

Pandit said an expedition he was on in 1991 peacefully came into contact with the island's inhabitants. "We jumped out of the boat and stood in neck-deep water, distributing coconuts and other gifts," Pandit said. "But we were not allowed to step onto their island."

The president of the nonprofit International Christian Concern told BBC News this was at least the third time Chau tried to meet with the tribe. "He was determined to reach these people with the Gospel and was deeply burdened for these guys," Jeff King said. "It was a sacrificial act. He knew it was dangerous."

Corry was critical of India's relaxation of controls over visitors to such islands. "The weakening of the restrictions on visiting the islands must be revoked, and the exclusion zone around the island properly enforced," he said.

He said the islanders should get the chance to determine their own fate. "All uncontacted tribal peoples face catastrophe unless their land is protected," he said.

An Indian police official earlier said they do not want to disturb the islanders' existence. "They are a treasure," said Dependera Pathak, director-general of police on the Andaman and Nicobar island groups. "We cannot go and force our way in. We don't want to harm them."

Indian officials said earlier that they were consulting anthropologists to see how they can approach with a friendly gesture. They watched the Sentinelese from a distance in recent days.

On Saturday the tribesmen were armed with spears and bows and arrows, but did not attempt to shoot them at the authorities.