Attorney Mari Newman (centre) talks with members of the media, as she stands with her plaintiffs and their supporters following a court hearing on same-sex marriage at the Federal District Court, in Denver. Picture: Brennan Linsley

Denver - A federal judge ruled on Wednesday that Colorado's ban on same-sex marriage was unconstitutional, but stayed his ruling until the issue is decided by a higher court.

US District Judge Raymond Moore found in favour of six same-sex couples who filed a lawsuit challenging the state's 2006 constitutional amendment that defined marriage as a union between one man and one woman.

Moore's 12-page ruling was the latest in a series of decisions by state and federal judges who have struck down state bans on gay marriage and then put their rulings on hold pending appeal.

Moore stayed his decision until August 25 to allow for appeals to higher courts.

Colorado Attorney General John Suthers said he was gratified the judge agreed that additional litigation in that court would be wasteful, since the US Supreme Court has been asked to hear an appeal in neighbouring Utah's case.

The Colorado law's status “will be decided by the Supreme Court's decision,” Suthers, a Republican, said in a statement.

Mari Newman, an attorney for the same-sex couples, said the attorney general's position was the only thing standing in the way of marriage equality for everyone in the state.

“It is time for him to back down from this losing battle and allow Colorado to treat all of its families with equality and dignity,” Newman said.

Emboldened by a landmark US appeals court ruling in June that found in favour of gay marriage in neighbouring Utah and which was itself put on hold, three county clerks in Colorado had begun issuing marriage licences despite a state ban on gay nuptials.

Colorado's Supreme Court last week ordered the Denver County clerk to stop issuing licences to same-sex couples pending the resolution of an appeal by the state attorney general.

Denver County Clerk Debra Johnson began handing out licences to gay couples on July 10, hours after a state judge backed a clerk in Boulder, Hillary Hall, who has issued more than 150 licences since late June.

Johnson took to Twitter to praise Moore's ruling: “It moved our nation even closer to the ultimate victory at hand: every couple treated equally under law. #COProud.” - Reuters