Pope Francis is set to offend American conservative Christians with the release of an explosive interview in which he slams their 'suicidal attitude.'

The pontiff's 60 Minutes episode will screen on Sunday and could strain his already-bad relations with the Roman Catholic Church in the US.

His sit-down with Norah O'Donnell was recorded on April 24.

He responded by saying a conservative is someone who 'clings to something and does not want to see beyond that.'

'It is a suicidal attitude,' he says, according to a transcript excerpt from CBS.

'One thing is to take tradition into account, to consider situations from the past, but quite another is to be closed up inside a dogmatic box.'

Francis has clashed with Christian conservatives almost since he was elected head of the church in 2013.

In December, he controversially approved letting Catholic priests bless same-sex couples

That radical policy shift aimed at making the church more inclusive while maintaining a ban on gay marriage.

In the interview, Francis defends the move, saying the blessing was for people, not 'the union' itself.

'Some people were scandalized by this. But why?' he asks.

He added that homosexuality was not a crime but a 'human fact.'