VATICAN CITY (AFP) - Pope Francis said Thursday he would set up a commission to study the possibility of women entering the Catholic clergy in his latest potentially historic opening on a vexed issue for the Church.

In apparently off-the-cuff remarks the 79-year-old pontiff promised to examine whether women could join the clergy at the rank of deacon, one below a priest.

The pledge came in a question and answer session with members of female religious orders during a meeting at the Vatican.

In the exchanges, Francis said he had discussed the use of female deacons in the early centuries of the Church with experts on the subject but was not clear as to their exact role and status.

"I believe, yes, it would do good for the Church to clarify this point," he said, in comments first reported by the National Catholic Reporter and confirmed by the Vatican's own newspaper Osservatore Romano.

"I am in agreement. I will speak (in favour of doing) something like this."

He later added: "It seems useful to me to have a commission that would clarify this."

Progressives in the Catholic Church have long argued that women are pitifully under-represented in the hierarchy, despite the number of women in religious orders (700,000) far outweighing the number of priests and monks combined (470,000).

Although deacons cannot celebrate mass on their own or hear confessions, they are ordained and can carry out many tasks in place of a priest, while remaining free to marry and have a family.

Deacon tasks can include presiding over baptisms, weddings and funerals as well as prayer services. They also often play a role in parish management and in offering pastoral guidance to believers.

Historians say women played this role in the first centuries of the Church, but the practice died out and calls for women to be allowed to become priests were categorically rejected by Pope John Paul II in 1994.

A commission charged with studying the term "deaconess" in 2001 concluded there was no basis for ordaining women to the role.

Francis' remarks appeared to have caught Vatican officials off-guard.

"I cannot confirm anything, until the full transcript of the conversation is published," his spokesman said. "These were off-the-cuff remarks."

The Pope's comments were warmly welcomed by the Women's Ordination Conference (WOC), a US-based group which lobbies for the Church to start appointing women to all levels of the clergy, as the Anglicans have done in recent decades.

"Opening a commission to study the diaconate for women would be a great step for the Vatican in recognising its own history," the organisation said in a statement.

WOC said the first women deacons were featured in the Bible and that there was "no scriptural barrier to women's priestly ordination."

A commission on the deacons issue "could begin to restore the Gospel values of equality and justice," it added.

Francis made it clear he did not see women being allowed to carry out the Eucharist, one of the central parts of the Catholic mass involving the consecration of the bread and wine that, for the faithful, represent the body and blood of Christ.

At this moment, prior to believers taking communion, priests are said to be in "Persona Christi" - representing the body of Christ, a role only men can perform.

Feminist Catholics reject the teaching that a male body is a necessary condition for representing the body of Christ.

"Upholding this discrimination as though it were the will of God, is simply indefensible," WOC said.

Francis has often championed the special qualities of the female sex, saying in December 2014: "Women are like strawberries on a cake - you always need more of them."

He has also repeatedly said since becoming pope in 2013 that he does not represent all Church teaching as being set in stone.

He has tried to make the global institution more understanding, less judgemental in its approach to divorced, cohabiting and gay believers.

Some critics say he has delivered little concrete change in the face of stiff resistance from Church conservatives.

But Vatican expert Marco Politi told AFP his latest comments were proof of his radical credentials.

"Francis feels time is passing and he has to make courageous decisions even if the majority of the Church's hierarchy is not ready to make these sort of changes".