Former UN ambassador Nikki Haley has moved closer to the widely-expected launch of her US presidential campaign - previewing a "big announcement" that looks certain to confirm her as an early rival to frontrunner Donald Trump in the race for the Republican nomination.

The move would make her just the second declared Republican candidate and could set the stage for a more combative phase of the campaign, potentially putting her in the sights of the former US president.

Ms Haley's campaign sent an email to supporters yesterday inviting them to a 15 February event in Charleston. There she will declare her candidacy, the sources said.

"My family and I have a big announcement to share with you on February 15th! And yes, it's definitely going to be a Great Day in South Carolina!" she tweeted, inviting supporters to turn out at an event in Charleston, the Palmetto State's largest town.

South Carolina is expected to host one of the first Republican nominating primaries in 2024 and will play an important role in picking the eventual candidate.

The daughter of two Indian immigrants, Nimrata "Nikki" Randhawa was raised in Bamberg, South Carolina as a Sikh, but now identifies as Christian. She is married to a South Carolina National Guard officer and has two children.

Ms Haley has gained a reputation in the Republican Party as a solid conservative who has the ability to address issues of gender and race in a more credible fashion than many of her peers.

She has also pitched herself as a stalwart defender of US interests abroad, having served as US ambassador to the United Nations under Mr Trump from 2017 to 2018.

During that time, the United States pulled out of the Iran nuclear deal, which was inked under Barack Obama and was highly unpopular among Republicans.

One Haley associate said she chose to launch her campaign this early to try to grab voters' attention and shake up a race that had so far been dominated by Trump and Florida Governor Ron DeSantis, who has not yet declared whether he will run.

Many key Republican donors and elected officials in South Carolina have been looking for alternatives to Mr Trump amid concerns about his electability, according to conversations in recent weeks with more than a dozen party officials and strategists.

Several prominent Republicans, including Ms Haley and US Senator Tim Scott, opted to skip a Trump campaign appearance in Columbia on Saturday, which was intended to showcase his support in the state.

Mr Scott, often considered a presidential contender himself, will kick off a "listening tour focused on Faith in America" in Charleston a day after Ms Haley's event, according to a campaign advisory. He will then swing through Iowa, another key early voting state.

Trump told reporters on Saturday that Haley had called himto say she was considering a run and that he told her "go byyour heart if you want to run," according to multiple mediareports.

AS US Ambassador to the UN, Nikki Haley addresses the UNSC at a meeting on Ukraine in 2018

Ms Haley received national attention in 2015 when, as governor, she signed a bill into law removing the Confederate battle flag from the grounds of the South Carolina state capitol, following the murder of nine black churchgoers by white supremacist Dylann Roof.

If she were to win the nomination, she would be the first woman at the top of the Republican presidential ticket in history, as well as the party's first non-white nominee.

Among her major challenges will be nailing down a consistent message. Even in a field where most candidates have changed their mind about key issues multiple times, Ms Haley is particularly chameleonic.

She has distanced herself from Mr Trump several times, only to later soften her rhetoric, saying he has an important role to play in the Republican Party.

While she has criticised Republicans for baselessly casting doubt on the results of the 2020 presidential election, she campaigned on behalf of multiple candidates who supported Mr Trump's false election fraud claims during the 2022 midterms.

Even as she has at times adopted a conciliatory message on racial issues, she often opts for a less measured tone. In November, she said at a campaign rally that Democratic Georgia Senator Raphael Warnock, a black man born in Savannah, should be "deported."

South Carolina is historically the third state to host the Republican nominating contest, and it often plays an outsized role in the race. Ms Haley, who governed the state from 2011 to 2017, is popular there, polls show.

Mr Trump and Mr DeSantis have both been active in the state.

While Ms Haley comes into the race as an underdog - most national polls show her support in the single digits - she is used to running from behind, having gained a reputation in political circles for coming out on top in tough-to-win races.