Francis has also suggested the question of women's ordination to the priesthood, controversially prohibited by Pope John Paul II in 1994, could be open to further study.

"Pastoral prudence must adequately discern whether there are forms of blessing, requested by one or several people, that do not transmit a mistaken conception of marriage," Francis wrote in a letter dated Sept. 25 and released by the Vatican on Oct. 2.

The pope's words come in response to five retired conservative Catholic cardinals who had written to the pontiff, expressing concerns about a number of hot-button issues that are expected to be discussed at a major Vatican meeting this month, known as the Synod of Bishops.