The Vatican said on Monday in a landmark ruling approved by Pope Francis that Roman Catholic priests can administer blessings to same-sex couples as long as they are not part of regular Church rituals or liturgies.

A document from the Vatican's doctrinal office said such blessings would not legitimise irregular situations but be a sign that God welcomes all.

It said priests should decide on a case-by-case basis and "should not prevent or prohibit the Church's closeness to people in every situation in which they might seek God's help through a simple blessing".

The pope hinted that an official change was in the works in October in response to questions put forward by five conservative cardinals at the start of a synod of bishops at the Vatican.

While the response in October was more nuanced, Monday's eight-page document, whose subtitle is "On the Pastoral Meaning of Blessings", spelled out specific situations. An 11-page section was titled "Blessings of Couples in Irregular Situations and of Couples of the Same sex".

The Church teaches that same-sex attraction is not sinful but homosexual acts are. Since his election in 2013, Francis has tried to make the 1.3 billion-member Church more welcoming to LGBT people without changing moral doctrine on same-sex activity.