Pope Benedict XVI has said same-sex marriage is unnatural, against human nature, and poses a threat to ‘justice and peace’.

In his message for World Day of Peace 2013, which was presented by the Holy See today (14 December), the Roman Catholic leader said there was a need to acknowledge and promote opposite-sex marriages as ‘natural’.

He said: ‘There is also a need to acknowledge and promote the natural structure of marriage as the union of a man and a woman in the face of attempts to make it juridically equivalent to radically different types of union.

‘Such attempts actually harm and help to destabilize marriage, obscuring its specific nature and its indispensable role in society.’

The pope’s message says anti-gay marriage views are not simply ‘truths of faith’, or the right to ‘religious freedom’, but ‘they are inscribed in human nature itself, accessible to reason and thus common to all humanity.’

He adds: ‘Efforts of this kind are all the more necessary the more these principles are denied or misunderstood, since this constitutes an offence against the truth of the human person with serious harm to justice and peace.’

In September, the pope said gay people are not fully developed humans because they do not obey Catholic law.

As a response to President Francois Hollande’s plan to bring in marriage equality in France, he said ‘the family is threatened in many places by a defection of human nature.’

Christian pop star Lady Gaga said gay people should not pay attention to what the Pope thinks of gay people.

She said: ‘What the Pope thinks of being gay does not matter. It doesn’t matter to the world. It matters to the people who like the Pope and follow the Pope.

‘It’s not a reflection of all Christians. It is not a reflection of all religious people. It’s a point of view of one person.’

Taking place on 1 January, the pope’s message for the World Day of Peace is called ‘Blessed are the Peacemakers’.