Same-sex unions are destroying the concept of marriage and of humanity itself, the powerful guardian of Roman Catholic doctrine said on Thursday.

"If the union of homosexuals is increasingly seen on the same level as marriage, we are facing the dissolution of the image of man," Cardinal Joseph Ratzinger said during a televised conference on the spiritual roots of Europe.

The debate over gay marriages has been making headlines in the United States and France and has become a hot political issue in both countries in recent months.

Last year, the Vatican condemned same-sex unions as deviant and a threat to society and Pope John Paul has since defended the institution of marriage as a union between man and woman.

Ratzinger, prefect of the Vatican's Congregation for the Doctrine of the Faith, said marriage was the nucleus of European identity, adding "Europe wouldn't be Europe anymore if this fundamental nucleus of its social structure disappeared."

"We all know how much marriage and family are being threatened," he said, citing an increase in same-sex unions as well as divorce and co-habitation as the main threats.

"With this tendency we're leaving the bounds of the history of human morality, which despite the various legal forms that marriage has taken was always essentially the communion between a man and a woman paving the way for children and family."