Republican former UN ambassador Nikki Haley suspended her White House campaign Wednesday, declining to endorse former president Donald Trump but calling on him to earn the support of moderates and independents who backed her in the primary.

"It is now up to Donald Trump to earn the votes of those in our party and beyond it who did not support him, and I hope he does that," Haley said in a televised address in Charleston, South Carolina.

Haley was in a two-person contest with Trump for the chance to face President Joe Biden in November's election but won just one state on "Super Tuesday" and never presented a serious obstacle in Trump's path to the nomination.

The 52-year-old was little known outside her native South Carolina before Trump tapped her as ambassador to the United Nations back in 2017 and used the high-profile UN post to cultivate an image as a plain-speaking conservative.

She prided herself on being the last challenger standing between the "chaos" of Trump and the 2024 Republican White House nomination.

"I am filled with the gratitude for the outpouring of support we've received from all across our great country," Haley added.

"But the time has now come to suspend my campaign. I said I wanted Americans to have their voices heard -- I have done that. I have no regrets." (AFP)