The father of John Chau, the US missionary killed when he attempted to land on North Sentinel Island to convert the inhabitants there, has hit out at the 'extreme Christianity' he blames for his son's death.

Interviewed by The Guardian, Dr Patrick Chau – like his son, a graduate of the evangelical Oral Roberts University in Oklahoma – said they had long been at odds over his missionary work and had agreed not to talk about it.

In his email comments he called religion 'the opium of the mass[es]', quoting Karl Marx, and said: 'If you have [anything] positive to say about religion l wish not to see or hear' it.

He said: 'John is gone because the Western ideology overpowered my [Confucian] influence. He said evangelicals' 'extreme Christianity' had driven his son to a 'not unexpected end'.

North Sentinel Island, part of the isolated Andaman group and administered by India, is home to a tribe which for decades has had little if any contact with outsiders. India has placed it out of bounds to visitors, fearing the introduction of disease. Chau had himself taken there by local fishermen and paddled ashore in a kayak. However, after twice attempting to approach the tribespeople he was killed on his third attempt.

All Nations, the organisation behind Chau's mission, told Christian Today it did not accept that North Sentinel Island ought to be isolated, that the landing was not illegal and that Chau had been well prepared for his venture.