Republican White House hopeful Mitt Romney said he did not support gay marriage or civil unions as US President Barack Obama finally stepped out to voice his backing for same-sex weddings.
"I do not favour marriage between people of the same gender and I don't favour civil unions if they're identical to marriage other than by name," Romney told a reporter for a local TV station in Denver.
"My view is domestic partnership benefit, hospital visitation rights and the like are appropriate, but the others are not," Romney added.
That stance is notably different from former Republican president George W. Bush who in 2004 said he supported civil unions, and argued his own party was wrong on the issue, although he remained opposed to same-sex marriage throughout his two terms in office.
Republican strategists have in the past used gay marriage as a "wedge" to inject cultural issues into narrow elections in swing states.
Obama became the first US president to say publicly he was in favour of same-sex marriage, in what supporters hailed as a historic moment for the fight for civil rights.
The US leader however also said the power to legalise gay marriage should be left to individual states.