Vice-president Joe Biden has strongly backed gay marriage in comments that appear to go beyond the "evolving" views of his White House boss.

Speaking on NBC's Meet the Press, Biden said he is "absolutely comfortable" with same-sex marriages, adding that homosexual couples are entitled to "the exact same rights" as heterosexual ones.

It makes him the most senior member of the administration to come out in favour of gay marriage and raises the hopes of many that a second Barack Obama term may lead to federal recognition of all unions, irrespective of sexual orientation.

Biden told Meet the Press: "I am absolutely comfortable with the fact that men marrying men, women marrying women and heterosexual men and women marrying one another are entitled to the same exact rights, all the civil rights, all the civil liberties."

The vice-president made it clear that the views were his personally, as opposed to that of the administration, prefacing the comments with "the president sets the policy".

But it comes as an indication that the White House is moving towards an official policy of backing same-sex marriage.

Asked outright if -Obama would support gay marriage in a second term, Biden said: "I don't know the answer to that."

The president has disappointed some in the LGBT community for not pushing hard enough for equal rights during his first four years in power.

Yesterday, at an event to mark the official launch of his 2012 re-election campaign, Obama trumpeted his record on gay rights, such as the removal of the "Don't Ask, Don't Tell" policy that encouraged gay members of the armed forces to hide their sexuality.

He told a crowd of supporters in Columbus, Ohio, that never again would America go back to the days when someone could get thrown out of the army because of "who you are or who you love".

But his views on gay marriage have not been as clear cut. He has stated in the past that he is in favour of same-sex unions, but has only gone as far as saying his views on gay marriage are "evolving".

Polling suggests that America has moved significantly on the issue over the past few years.

A Pew Research Centre survey last month noted that 47% of people are now in favour of same-sex marriage, with 43% against. The same poll taken during the last presidential campaign found that 51% were against allowing gays and lesbians to wed, with 39% in favour.

Other polls have suggested that over the last 12 months, the scales have tipped further, with a majority of Americans now in favour of gay marriage.

During the Meet the Press interview, Biden said the portrayal of gay people on TV shows such as Will & Grace had helped shaped society's views in recent years.

The trajectory comes in contrast to that of the presumptive Republican presidential candidate for the White House, Mitt Romney.

In his earlier political career, the former Massachusetts governor backed equal rights for gay and lesbian couples wanting to marry.

In a 1994 letter to gay members of the Log Cabin Republicans he talked of his support for "full equality for America's gay and lesbian citizens", stating that he would have a better record on the issue than his opponent, the late Democratic senator Edward Kennedy.

But the Republican race for a White House nod has seen him pull his views to the right on social issues, and he now believes that marriage can only be between a man and a woman.

Biden's strong words in favour of gay marriage could be seen as a test of reaction ahead of a potential similar move by Obama.

In a tweet, the president's campaign strategist David Axelrod denied that the two men differed on the subject.

"What VP said – that all married couples should have exactly the same legal rights – is precisely POTUS's (the president's) position," he posted.

Nonetheless, gay rights campaigners seized on the vice-president's comments to pressure Obama further on the issue.

Joe Solmonese, president of the Human Rights Campaign, said he was "encouraged" by the development, adding: "Now is the time for President Obama to speak out for full marriage equality for same-sex couples."