The US government said it will recognise same-sex marriages in Utah even though the state itself will not.
It also pledged to provide benefits to around 1,400 same-sex couples who married in the state before the Supreme Court halted nuptials in early January.
On 20 December last year, a federal judge in Utah briefly allowed same-sex marriages, but the Republican governor Gary Herbert said on 8 January the marriages would no longer be legal, for now.
Two days later, the US Justice Department confirmed that the marriages will continue to be lawful.
“These marriages will be recognised as lawful and considered eligible for all relevant federal benefits on the same terms as other same-sex marriages,” US Attorney General Eric Holder said in a statement.
“These families should not be asked to endure uncertainty regarding their status as the litigation unfolds,” he added.
Brian Brown, the President of the National Organisation for Marriages which opposes same-sex marriages, said the move was “outrageous” and undermined federal authority.
“It is the right of states to determine marriage, and the voters and legislature of Utah have done just that,” he said in a statement.
Utah temporarily became the eighteenth US state to legalise same-sex marriage when US District Judge Robert Shelby ruled that a voter-passed amendment to the state's constitution that defined marriage as exclusively between opposite sexes was unconstitutional.
The US Supreme Court on Monday put that lower-court ruling on hold, at the request of Utah officials, halting gay weddings in Utah while the state appeals Shelby's decision to the Denver-based 10th US Circuit Court of Appeals.
LGBT rights advocates sent a letter to Mr Holder on Thursday asking for the federal government to recognise same-sex marriages that had been performed in Utah, and for the benefits such as tax breaks that go along with official legal status.
Michele Poast, a newly-wed, was on the telephone to the Veterans Administration to secure benefits for her and her wife Angela Hinton’s children after they heard the news.
“It's a validation,” said Ms Hinton, 41, who was married on 23 December.
“I mean, yes, we've been doing this thing together the whole time, but now it's officially recognised that you're a parent, a wife, a spouse.”
Chad Griffin, President of Human Rights Campaign said: “This is only the beginning of this fight, and this work continues until marriage equality returns to Utah for good, and full equality reaches every American in all 50 states.”
Additional reporting by Reuters