Pope Francis has approved new rules to allow priests to bless same-sex couples, a significant advance for LGBT people in the Roman Catholic Church.

The changes have come to light in a new document which explains the decision, insisting that people seeking God’s love and mercy shouldn’t be subject to “an exhaustive moral analysis” to receive it.

The leader of the Roman Catholic Church said priests should be permitted to bless same-sex and "irregular" couples, under certain circumstances.

However, in the document that was published today, the Pope said that such blessings should not be part of regular Church rituals or related to civil unions or weddings.

It also added that its definition of marriage was a lifelong sacrifice between a man and a woman.

The Vatican said the change should be a sign that "God welcomes all", however the decision of whether to allow the blessings would be operated on a case-by-case basis.

“Ultimately, a blessing offers people a means to increase their trust in God,” the document said.

“The request for a blessing, thus, expresses and nurtures openness to the transcendence, mercy, and closeness to God in a thousand concrete circumstances of life, which is no small thing in the world in which we live.”