Hillary Clinton made a lighthearted Twitter debut, poking fun at her own image and fuelling speculation about what the future holds for the former secretary of state.

Washington - Former US secretary of state Hillary Clinton, who may be eyeing a run in the 2016 presidential election, came off the sidelines on Monday and announced her support for gay marriage.

While Clinton pushed gay, lesbian and transgender (LGBT) rights during her four-year tenure as America's top diplomat, considering them human rights, she had not until now advocated for same-sex marriage.

“LGBT Americans are our colleagues, our teachers, our soldiers, our friends, our loved ones. And they are full and equal citizens, and deserve the rights of citizenship. That includes marriage,” she says in a nearly six-minute video.

“That's why I support marriage for lesbian and gay couples. I support it personally and as a matter of policy and law, embedded in a broader effort to advance equality and opportunity for LGBT Americans and all Americans.”

The video was released by the Human Rights Campaign, a civil rights organisation working for gay rights.

It came just days after Clinton's husband, former US president Bill Clinton, urged the Supreme Court to overturn a bill he signed in 1996 defining marriage as a union between a man and a woman, calling it “discriminatory”.

White House spokesperson Jay Carney, asked for President Barack Obama's views on the statement by his former top diplomat, told reporters: “The president believes that any time a public official of stature steps forward to embrace a commitment that he shares to equality for LGBT Americans, he thinks it's a good thing.”

During her failed 2008 White House bid, Hillary Clinton stopped short of endorsing gay marriage, favouring civil unions instead.

In the video, she acknowledges that “like so many others, my personal views have been shaped over time”, saying they had been changed by conversations and personal experiences, as well as “by the guiding principles of my faith”.

“Marriage after all is a fundamental building block of our society, a great joy and yes, a great responsibility,” Clinton says.

“To deny the opportunity to any of our daughters and sons solely on the basis of who they are and who they love is to deny them the chance to live up to their own God-given potential.”

Clinton stepped down on February 1, and polls show that if she throws her hat into the ring to be the Democratic Party nominee in the 2016 election, she would have a strong edge over any other candidate.

“She is in both parties right now by far, I think, the most interesting candidate, probably the strongest candidate,” Obama's former White House election aide David Plouffe said during a Sunday interview. - Sapa-AFP