Indian authorities have admitted that they will struggle to recover the body of an American Christian missionary who was killed after wading ashore on an island cut off from the modern world.

John Allen Chau was killed last week by North Sentinel islanders who shot him with arrows and then buried his body on the beach.

Now officials have admitted that even they don't travel to North Sentinel, as the people who live there still live as their ancestors did thousands of years ago and view outsiders with suspicion.

Chau was a preacher who had visited the Andaman and Nicobar islands in the past, a police source said

Dependera Pathak, director-general of police on India's Andaman and Nicobar Islands, where North Sentinel is located, said: 'It's a difficult proposition. We have to see what is possible, taking utmost care of the sensitivity of the group and the legal requirements.'

He added that police are now consulting anthropologists, tribal welfare experts and scholars to figure out a way to recover the body.

While visits to the island are heavily restricted, Chau paid fishermen last week to take him near North Sentinel, using a kayak to paddle to shore and bringing gifts including a football and fish.

Chau took a boat ride with the fishermen before venturing alone to North Sentinel Island (pictured, a file photo shows tribesmen on the island)

The North Sentinel island is out of bounds even to the Indian navy in a bid to protect its reclusive inhabitants who number only about 150

The Sentinelese tribe has attacked almost everyone who has entered their territory. Pictured, the tribes people are seen wielding arrows on the island

P.C Joshi, an anthropology professor at Delhi University who has studied the islands said that Chau 'invited aggression' and 'it was 'a foolish adventure'.

Joshi noted that the visit not only risked Chau's life, but also the lives of islanders who have little resistance to many diseases.

'They are not immune to anything. A simple thing like flu can kill them,' he said.

On his first day Chau interacted with some tribesmen - who survive by hunting, fishing and collecting wild plants - until they became angry and shot arrows at him.

The 26-year-old self-styled adventurer and Christian missionary then swam back to the fishermen's boat waiting at a safe distance.

He revealed that a boy, who he believed to be ten years old, shot him with an arrow that hit the bible he had clutched to his chest

American adventurer John Allen Chau, right, stands for a photograph with Founder of Ubuntu Football Academy Casey Prince, 39, in Cape Town, South Africa, days before he left for the remote Indian island of North Sentinel Island

That night, he wrote about his visit and left his notes with the fishermen.

He returned to North Sentinel the next day, November 16.

What happened next isn't known exactly, but on the morning of the following day, the fishermen watched from the boat as tribesmen dragged Chau's body along the beach and buried his remains.

Pathak said seven people have been arrested for helping Chau, including five fishermen, a friend of Chau's and a local tourist guide.

Chau was apparently shot and killed by arrows, but the cause of death can't be confirmed until his body is recovered, Pathak said.

He also said the police were examining whether Chau had tried earlier to visit the isolated island.

He returned two days later better prepared. He left a dinghy midway and took a canoe to the island alone

Pathak said Chau and his accomplices planned well for last week's visit by 'camouflaging the visit as fishing.'

Chau even appeared to be full of confidence in his notes, writing: 'God sheltered him from coastguard and Navy.'

In an Instagram post, his family said it was mourning him as a 'beloved son, brother, uncle and best friend to us.' The family also said it forgave his killers and called for the release of those who assisted him in his quest to reach the island.

'He ventured out on his own free will and his local contacts need not be persecuted for his own actions,' the family said.

The Sentinelese tribe are an indigenous tribe who live on North Sentinal Island, lies around 450 miles from the coast of Thailand and more than 745 miles from mainland India

Authorities say Chau arrived in the area on October 16 and stayed on another island while he prepared to travel to North Sentinel.

It was not his first time in the region: he had visited the Andaman islands in 2015 and 2016.

With help from a friend, Chau hired fishermen for $325 to take him there on a boat, Pathak said.

After the fishermen realized Chau had been killed, they left for Port Blair, the capital of the island chain, where they broke the news to Chau's friend, who in turn notified his family, Pathak said.

Police surveyed the island by air Tuesday, and a team of police and forest department officials used a coast guard boat to travel there Wednesday.

Another trip was planned for Thursday.

The Chau family posted this statement regarding his death on his Instagram account on Wednesday

Anthropology professor at Delhi University P.C. Joshi says that even minor influences can kill them the North Sengalese islanders

India has a hands-off approach to the island's people. Tribespeople killed two Indian fishermen in 2006 when their boat broke loose and drifted onto the shore, but Indian media reports say officials did not investigate or prosecute anyone in the deaths.

India recently changed some of its rules on visiting isolated regions in the Andamans.

While special permits are required, scholars say visits are now theoretically allowed in some parts of the Andamans where they used to be entirely forbidden, including North Sentinel.

Chau had no permit, police said.

Chau had wanted to go to North Sentinel to share Christianity with the indigenous people since high school.

Mat Staver, founder and chairman of Covenant Journey, a program that takes college students on tours of Israel to affirm their Christian faith, said Chau went through that program in 2015.

The Sentinelese attracted international attention in the wake of the 2004 Asian tsunami, when a member of the tribe was photographed on a beach, firing arrows at a helicopter (pictured)

'He didn't go there for just adventure. I have no question it was to bring the gospel of Jesus to them,' Staver said.

Staver said Chau's last notes to his family on November 16 told them that they might think he was crazy but he felt it was worth it and asked that they not be angry if he was killed.

Before attending Oral Roberts University, Chau had lived in southwestern Washington state and went to Vancouver Christian High School.

Phone messages left with relatives were not immediately returned Wednesday.

In this November 14, 2005 file photo, clouds hang over the North Sentinel Island, in India's southeastern Andaman and Nicobar Islands