US justices wary of broad ruling endorsing gay marriage

US Supreme Court justices signalled on Tuesday that they are reluctant to embrace a broad ruling finding a fundamental right to marriage for gays and lesbians across the US.

As sign-waving demonstrators massed outside, the court completed more than an hour of oral argument on whether to let stand a California ban on same-sex marriage without indicating a clear path forward.

Swing vote Justice Anthony Kennedy raised concerns about the court entering "uncharted waters" on an issue that divides the states. Kennedy even raised the prospect of the court dismissing the case, a relatively unusual move that would leave intact a federal Appeals Court ruling that struck down the law, known as Proposition 8.

In a similar vein, Justice Samuel Alito also urged caution, noting that gay marriage as a concept is "newer than cellphones and the internet". None of the justices indicated support for the Obama administration's favoured solution, which would strike down Proposition 8 and require the other eight states that already recognise civil unions or domestic partnerships to allow gays and lesbians to marry.