Pope Benedict yesterday denounced the "powerful political and cultural currents" seeking to legalise gay marriage in the United States.

The Pope's latest comments in opposition to homosexual marriage came in an address to bishops from several midwestern states on a regular visit to the Vatican.

"Sexual differences cannot be dismissed as irrelevant to the definition of marriage," he said.

He added the traditional family and marriage had to be "defended from every possible misrepresentation of their true nature" because, he said, whatever injured families injured society.

"In this regard, particular mention must be made of the powerful political and cultural currents seeking to alter the legal definition of marriage (in the United States)," he added.

Last week, Maryland legalised same-sex marriage. Massachusetts, Iowa, Vermont, New Hampshire, Connecticut, New York and the District of Columbia allow gay and lesbian weddings.

Washington state will join the list in June unless opponents stop it ahead of a possible referendum, and Maryland will be added in January 2013 unless its law, too, is overturned by a possible referendum.

An appeals court overturned California's ban on gay marriage, enacted through a 2008 referendum.

Benedict called on American bishops to continue their "defence of marriage as a natural institution consisting of a specific communion of persons, essentially rooted in the complementarity of the sexes and oriented to procreation".

Gay marriage is legal in a number of European countries, including Spain and the Netherlands.