Supporters and opponents demonstrating outside the Supreme Court
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Gay marriage: US Supreme Court debates Defense of Marriage Act

A US law that defines marriage as between a man and a woman only has been sharply criticised by a number of Supreme Court justices at a landmark hearing.

The constitutionality of the Defense of Marriage Act (Doma) was questioned by the four liberal justices on the nine-member court, but also by one of their colleagues, regarded as a possible swing voter

Legal analysts speculated the panel may strike down the law, which denies gay couples various federal benefits.

A ruling on the case is expected by the end of June.

From Washington, Steve Kingstone reports.

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