Vatican has played down expectations that Pope Francis might be ready to ordain women as deacons after he had raised hopes among liberal Catholics by promising to set up a commission to study the issue.

Deacons are ordained clerics who sit just behind priests in the Church hierarchy. They can officiate at baptisms, funerals and weddings, but are not allowed to celebrate Mass, hear confessions or anoint the sick.

The role is reserved for men, who, unlike priests, can be married. During a question-and-answer session with nuns on Thursday, the Pope was asked if a commission could be created to study whether women might also serve as deacons.

"It would be good for the church to clarify this point. I agree," the Pope replied, setting off a mammoth debate that spilled out into the media on whether Francis was poised to rock the Church and crack open the all-male clergy.

But 24 hours after Francis's comments, Vatican spokesman Federico Lombardi moved to head off any such speculation.

"One has to be honest. The Pope did not say that he had any intention of introducing ordination for female deacons, much less priestly ordination for women," he told Vatican radio.

"It would be mistaken to reduce the many important things that the Pope said to the nuns to this single question."

The Church teaches that women cannot become priests because Jesus willingly chose only men as his apostles. However, St. Paul refers in the bible to a deaconess called Phoebe, leading liberal Catholics to argue that there is clear precedent for women to play a much more important role in Church life.

Conservative Catholics would certainly put up fierce resistance to any such a move, eager to preserve clear and separate roles for men and women within the Church.

After his election in 2013, Pope Francis swiftly ruled out ordaining women priests. However, he stirred concern among traditionally minded Catholics over what they perceive as his liberal leanings on a range of other issues, from divorce to the use of contraception.

Earlier this year, he overturned centuries of tradition that banned women from a foot-washing service during Lent, upsetting conservatives and delighting women's rights activists.

Church liberals had hailed his call for a commission to look into the question of deacons.

"I can't underscore enough how groundbreaking this is for the Church," said Father James Bretzke, Professor of Moral Theology at the Boston College School of Theology and Ministry.

"It's clear that Pope Francis, I believe, is trying to move toward institutionalising a greater leadership and service role for women in the Church," he added in emailed comments.

The Vatican did not say when the promised commission would be set up or what it would be asked to do.