New Delhi (CNN) An American Christian believed to have been engaged in missionary work appears to have been killed by tribespeople from one of the world's most isolated communities, on a remote island hundreds of miles off the coast of India, according to officials.

The 27-year-old American, identified as John Allen Chau , came to India on a tourist visa but came to the Andaman and Nicobar islands in October with the express purpose of proselytizing, Dependra Pathak, director general of police of the Andaman and Nicobar islands, told CNN.

"We refuse to call him a tourist. Yes, he came on a tourist visa but he came with a specific purpose to preach on a prohibited island," Pathak said.

Chau did not inform the police of his intentions to travel to the island to attempt to convert its inhabitants, officials said.

The adventurer's relatives, in a post on his Instagram page, said Wednesday that Chau was a beloved family member. "To others he was a Christian missionary, a wilderness EMT, an international soccer coach, and a mountaineer. He loved God, life, helping those in need, and had nothing but love for the Sentinelese people." The family said it forgives those who took Chau's life.

The island, North Sentinel Island, is inhabited by the Sentinelese, who are protected under Indian law. Just more than a dozen people are officially thought to live on the remote island in the Andaman and Nicobar archipelago.

The island is a protected area, and people are not allowed to go within 5 nautical miles of it, after previous incidents of aggressive behavior toward outsiders were observed. In 2006, two local fishermen were killed by the tribes.

Illegal access

Pathak said the American missionary had asked one of his local friends, an electronic engineer, to arrange a boat and find some fishermen who could take him to the island. The contact found a boat and the fishermen, along with a water sports expert, to help with the expedition.

All seven locals who facilitated the trip have been arrested.

"According to the fishermen, they used a wooden boat fitted with motors to travel to the island on November 15," Pathak said.

"The boat stopped 500-700 meters (1,640 - 2,300 feet) away from the island and (the American missionary) used a canoe to reach the shore of the island. He came back later that day with arrow injuries. On the 16th, the (tribespeople) broke his canoe.

Chau was a world traveler who was also a staunch Christian.

"So he came back to the boat swimming. He did not come back on the 17th; the fishermen later saw the tribespeople dragging his body around."

The police haven't independently verified that he is dead, but based on what the fishermen have told them believe that he was killed.

"We have a team out in the waters for reconnaissance and to strategize how to recover his body. The team consists of coastal guards, officials from tribal welfare department, forest department officers and police officials."

Remote, largely isolated

An official from the US Consulate in Chennai confirmed that diplomats are "aware of reports concerning a US citizen in the Andaman and Nicobar Islands."

"When a US citizen is missing, we work closely with local authorities as they carry out their search efforts. Due to privacy considerations, we have no further comment," the official said.

Chau was "martyred," said Mat Staver, founder and chairman of Covenant Journey, a Christian ministry that introduces college-age students to Israel through an immersion program.

"John loved people, and he loved Jesus. He was willing to give his life to share Jesus with the people on North Sentinel island," Staver said in a press release. "Ever since high school, John wanted to go to North Sentinel to share Jesus with this indigenous people."

The island group is about 850 miles (1,370 kilometers) east of the Indian subcontinent.

There are 572 islands in the Andaman and Nicobar Islands territory, only three dozen of which are inhabited. The territory has a population of nearly 380,000, according to India's 2011 census.

The 2011 survey only spotted 15 Sentinelese on their island -- the count was done from a distance due to the danger in approaching the tribe. In the 2001 census, the total population was estimated to be 39.

India has designated five indigenous tribal groups in the territory as "particularly vulnerable" due to the loss of sustaining resources and customs.

India's Ministry of Tribal Affairs has said that, with regard to Sentinelese tribes, the Andaman and Nicobar Islands administration "has adopted an 'eyes-on and hands-off' policy to ensure that no poachers enter into the island."

Survival International, a nongovernmental group that says it is dedicated to tribal peoples' rights, said Indian authorities should ensure outsiders not make contact with the tribe, because of the risk of disease or threats to their land.

"The Sentinelese have shown again and again that they want to be left alone, and their wishes should be respected," the group said. "The British colonial occupation of the Andaman Islands decimated the tribes living there, wiping out thousands of tribespeople, and only a fraction of the original population now survive. So the Sentinelese fear of outsiders is very understandable."