REYKJAVIK (AFP) - Iceland Prime Minister Johanna Sigurdardottir married her long-time partner on Sunday as a new law legalising homosexual marriages came into force.

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Sigurdardottir, in her late 60s, formally married writer Jonina Leosdottir after the couple submitted a demand for their civil union to be transformed into a marriage, the RUV broadcaster said.

Iceland's parliament on June 12 unamimously adopted legislation allowing gay marriage, in a law that came into force on Sunday.

Homosexual couples could previously enter into a civil partnership and benefit from the same rights as heterosexual couples, but this had not been considered a formal marriage.

Sigurdardottir, born in 1942, took power in February 2009. She has lived with Ledsdottir, who is in her fifties, for several years and the couple entered a civil union in 2002.

She is the country's first openly gay head of government.