Former US Secretary of State Hillary Clinton is expected to formally declare her run for the 2016 Democratic presidential nomination shortly.
Mrs Clinton, who also served as a senator for New York, ran for the Democratic presidential nomination in 2008 but lost to Barack Obama.
The overwhelming Democratic favourite, she has been expected to declare her candidacy for months.
Mrs Clinton was also first lady when her husband Bill Clinton was president.
She is expected to declare via social media.
Analysis – Anthony Zurcher, BBC North America reporter, Washington DC
This time around, Mrs Clinton’s path to the Democratic nomination appears much easier. Unlike 2008 there’s no inspirational, once-in-a-generation opponent like Mr Obama waiting in the wings.
There’s not even a charismatic, battle-tested candidate like former vice presidential nominee John Edwards or a Hispanic governor with foreign policy chops like Bill Richardson in the field.
But if Mrs Clinton’s nomination campaign will be easier, actually winning the presidency could be just as difficult – or more so.
Unlike 2008, the Democratic nominee will be defending eight years of her party’s rule, with all the baggage that comes with it.
Instead of facing a Republican Party on its heels, fresh from massive losses in both chambers of Congress, a nominated Mrs Clinton will have to defeat a Republican candidate with the political wind at his back.
Mrs Clinton, 67, is expected to release a video outlining her campaign themes but will put off a large, formal speech.
She will then travel to Iowa and New Hampshire, two early primary contests in the 2016 race.
After her failed nomination bid in 2008, Mrs Clinton served as secretary of state in Mr Obama’s first administration (2009-2013).
Known for her punishing travel schedule – she visited 112 countries in four years – she led the US response to the Arab Spring and the military intervention in Libya in 2011.
She has been harshly criticised by Republicans in Congress over her handling of the 2012 raid on the US consulate in the Libyan city of Benghazi in which the US ambassador was killed.
As a senator, Mrs Clinton voted for the invasion of Iraq in 2003 but distanced herself from the way the war was waged, and called for US troops to be withdrawn.
During her husband’s first term as president, she campaigned for healthcare reform but her plan fell apart and never made it to a vote in Congress.
She was also embroiled in the some of the scandals which marred her husband’s presidency, becoming the only US first lady to be called to testify before a grand jury.
Mrs Clinton stood by her husband when he was exposed as having had an affair with a White House intern, Monica Lewinsky.