US President Barack Obama has ended months of equivocation on the issue of gay marriage by saying he thinks same-sex couples should be able to wed.
He told ABC News: "It is important for me to go ahead and affirm that I think same-sex couples should be able to get married."
Mr Obama has become the first US president to back gay marriage.
In recent days, Vice-President Joe Biden and cabinet member Arne Duncan had expressed support for gay unions.
The interview with ABC News' Robin Roberts was apparently hastily arranged as Mr Obama came under mounting pressure to clarify his position on the issue.
During the ABC interview, which airs later on Wednesday, Mr Obama pointed to his administration's commitment to increasing rights for gay citizens.
He cited the repeal of the military's 'don't ask, don't tell' policy and said his administration had dropped support for the Defense of Marriage Act.
"I've stood on the side of broader equality for the LGBT community. I hesitated on gay marriage in part because I thought civil unions would be sufficient," Mr Obama said.
He added: "I was sensitive to the fact that for a lot of people, the word 'marriage' was something that evokes very powerful traditions, religious beliefs and so forth.
"But I have to tell you that over the course of several years as I talked to friends and family and neighbours, when I think about members of my own staff who are in incredibly committed monogamous relationships, same-sex relationships, who are raising kids together, when I think about those soldiers or airmen or marines or sailors who are out there fighting on my behalf and yet feel constrained, even now that 'don't ask don't tell' is gone, because they are not able to commit themselves in a marriage," Obama said.
"At a certain point, I've just concluded that for me personally it is important for me to go ahead and affirm that I think same-sex couples should be able to get married."
In 2010, Mr Obama said his views on the issue were "evolving", a stance that had frustrated gay rights supporters and donors.
His comments came a day after North Carolina approved a constitutional amendment effectively banning same-sex marriage or civil unions.
Before that vote, the Obama campaign had opposed the measure, which was passed with 61% in favour and 39% against.
While Mr Obama is the first US president to support gay marriage, correspondents said the president's views on gay marriage were likely to upset some voters.
Some African-American voters oppose same-sex marriage on religious grounds.
Mitt Romney, the Republican candidate who is all but certain to challenge Mr Obama for the White House in November's elections, reiterated that he did not support gay marriage.
The former Massachusetts governor told a Fox News affiliate: "I indicated my view, which is I do not favour marriage between people of the same gender, and I do not favour civil unions if they are identical to marriage other than by name.
"My view is the domestic partnership benefits, hospital visitation rights, and the like are appropriate but that the others are not."
A Gallup poll on Tuesday suggested that 50% of Americans were in favour of legalising gay marriage - a slightly lower proportion than last year - while 48% said they would oppose such a move.