The Vatican has sought to tamp down discord over Pope Francis' backing last month for same-sex civil unions, reiterating that he did not question the Catholic dogma of marriage being between a man and a woman.

A note sent to papal ambassadors late last week by the Secretariat of State – the Vatican's highest bureaucratic authority – hammered home that there had been no chance in Church doctrine.

"It's clear that Pope Francis was referring to certain arrangements by states, certainly not to Church doctrine, which has often been reaffirmed over the years," the authority said in the document, published by envoy to Mexico Archbishop Franco Coppola among others.

Italian Catholic newspaper Avvenire reported that the letter had been intended for circulation to bishops around the world.

In a documentary that premiered at the Rome Film Festival last month, Francis stunned many with his comment that gay couples should be allowed to have legally recognised civil unions.

"These are children of God, they have the right to a family," the Argentine pontiff said. "What we have to create is a law of civil union, they have the right to be legally protected."

The quotes shown in a film by documentarist Evgeny Afineevsky were originally recorded as part of an interview Francis gave to a Mexican journalist in 2019 but had never before been shown.

Their release sparked fears among some traditionalists that the pope might in fact favour gay marriage.

Ultra-conservative German Cardinal Gerhard Mueller, a former Vatican head of dogma retired by Francis in 2017,  said he had received calls from "disturbed" fellow Catholics.

"The pope is not above God's word," he told an Italian daily.