The Pope has used his annual Christmas address to attack same-sex marriage, accusing gay people of "manipulating their nature" to suit their sexual choices.

Pope Benedict XVI dedicated his speech to "family values", saying that the traditional unit was under attack as same-sex marriage legislation gathers support in the UK, US and France.

He told the Vatican bureaucracy: "In the fight for the family, the very notion of what being human really means is being called into question," translated AFP.

He insisted gender theories were invalid, adding that people were essentially wrong to "choose" an identity that went against their nature.

In particular 85-year-old refuted Simone de Beauvoir's gender theory, one of the pioneering philosophies of feminism, which argues that "a woman is not born a woman but becomes one," and that gender is separate from anatomy.

He told the Vatican: "People dispute the idea that they have a nature, given to them by their bodily identity, that serves as a defining element of the human being," he said, reported the Associated Press.

"They deny their nature and decide that it is not something previously given to them, but that they make it for themselves."

"The manipulation of nature, which we deplore today where our environment is concerned, now becomes man's fundamental choice where he himself is concerned," he said, according to the Associated Press.

It is the second time the Pope has attacked same-sex marriage in the space of a week. In his recently released annual peace message he claimed gay marriage, abortion and euthanasia are threats to world peace.

In his latest attack he even quoted a study by France's chief rabbi, which claimed that gay marriage would have a negative effect on family life. This could signal the beginnings of an interfaith alliance against same-sex marriage, reported The Independent.

The Vatican press machine is well-oiled of late, with the Pope writing his first article for a secular newspaper on Friday, advising in he Financial Times that Christmas is a time for both joy and "deep reflection."

Additionally despite a somewhat eccentric launch of his Twitter account (he follows seven versions of himself and it was a week before he sending his first tweet), the Vatican have crowed that the Twitter account is a holy success.

In an unusual comparison, they pointed out the Pope had more retweets than Canadian popster Justin Bieber, despite having an army of followers on Twitter.

In a surreal article, the Vatican newspaper performed a comparative breakdown between Bieber an the Pope, reported Reuters.

The article noting that about 50% of the pope’s followers had retweeted his first post compared with a measly 0.7% of Belibiebers who re-tweeted one of the singer’s most popular tweets on September 26, after he posted about the death of a six-year-old.