Pope Francis, making permanent a temporary measure put in place for the Vatican's jubilee year, declared today that all priests would have the right to forgive abortion.

'I henceforth grant to all priests, in virtue of their ministry, the faculty to absolve those who have committed the sin of procured abortion,' the pope wrote in an apostolic letter marking the end of the 'Year of Mercy', which wound up yesterday, AFP reported.

'The provision I had made in this regard, limited to the duration of the Extraordinary Holy Year, is hereby extended, notwithstanding anything to the contrary,' he wrote.

The 79-year old Argentine said he had to 'restate as firmly as I can that abortion is a grave sin, since it puts an end to an innocent life'.

Yesterday, as he brought the jubilee to an end by closing the bronze-panelled Holy Door in Saint Peter's Square, Francis gave an interview in which he slammed abortion as "a horrendous crime".

But he said today that the end of the special year did not mean the end of mercy itself, and so-called sinners must be given a chance to repent. The Church considers abortion to be a sin.

'May every priest, therefore, be a guide, support and comfort to penitents on this journey of special reconciliation,' the pope wrote.