The Vatican said the bishop would be "relieved" of his duties as a result of investigations at his Diocese of Tyler.

Bishop Strickland is a leading voice in a branch of US Catholicism that is opposed to the Pope's reforms.

His removal comes after Francis spoke of the "backwardness" of some US Catholic church leaders.

Bishop Strickland has launched a series of attacks on the Pope's attempts to update the Church's position on social matters and inclusion, including on abortion, transgender rights and same-sex marriage.

In July, he warned that many "basic truths" of Catholic teaching were being challenged, including what he called attempts to "undermine" marriage "as instituted by God" being only between a man and a woman.

He criticised as "disordered" the attempts of those who "reject their undeniable biological God-given identity".

His letter suggested that attempts to change "that which cannot be changed" would lead to an irrevocable schism in the Church. Those seeking change, he warned, "are the true schismatics".

Bishop Strickland was under investigation by the Vatican and had previously declined the opportunity to resign, and in an open letter in September challenged the Pope to fire him.

"I cannot resign as Bishop of Tyler because that would be me abandoning the flock," he said.

The right-wing "Coalition for Canceled Priests" held a conference earlier this year to support him during the investigation.