Pope Francis has appeared to leave open the possibility of priests blessing same-sex couples, if they are limited, decided on a case-by-case basis and not confused with wedding ceremonies of heterosexuals.

Francis made his opinion known in one answer to five questions from five conservative cardinals from Asia, Europe, Africa, the United States and Latin America.

The cardinals sent the pope a set of formal questions, known as "dubia" ("doubts" in Latin), about issues relating to a global gathering that starts at the Vatican on Wednesday.

One of the questions specifically regarded the practice, which has become relatively common in places like Germany, of priests blessing same sex couples who are in a committed relationship.

The written exchange took place in July and the Vatican published the pope's responses on Monday after the five cardinals unilaterally disclosed their initiative, saying they were not satisfied with Francis' answers.

The pope's nuanced response differed from an explicit ruling against such blessings by the Vatican's doctrinal office in 2021.

In his seven-point response, Francis said the Church was very clear that the sacrament of matrimony could only be between a man and woman and open to procreation and that the Church should avoid any other ritual or sacramental rite that contradicted this teaching.

Still, he said "pastoral charity should permeate all our decisions and attitudes" adding that "we cannot be judges who only deny, reject and exclude".

At times, he said, requests for blessings were a means through which people reached out to God to live better lives, even if some acts were "objectively morally unacceptable".

The Church teaches that same-sex attraction is not sinful but homosexual acts are.

Any eventual blessings, Francis said, should not become the norm or get blanket approval from Church jurisdictions such as dioceses or national bishops conferences.

Francis DeBernardo, executive director of New Ways Ministry, which promotes Church outreach to LGBT Catholics, said that while the response was not a "full-fledged, ringing endorsement" of such blessings, it was very welcomed.

In a statement DeBernardo said that the pope's words implied "that the church does indeed recognise that holy love can exist between same-gender couples, and the love of these couples mirrors the love of God".