Republican presidential hopeful Nikki Haley has called her rival Donald Trump "insecure" after he spread false claims that she is not eligible to be US president.
The former president shared a "birther" conspiracy theory questioning her eligibility because her parents were not born in the country.
But Ms Haley was born in the US, which means she can run for office.
Asked about the attacks on CNN, Ms Haley said: "I know President Trump well...That's what he does when he feels threatened".
She added: "That's what he does when he feels insecure."
For years, Mr Trump pushed a false conspiracy theory that President Barack Obama, who was born in Hawaii, had forged his birth certificate and was born in Kenya.
Ms Haley is Mr Trump's closest rival in the next contest of the Republican race to be the party's presidential nominee. Voters in New Hampshire will select their candidate on Tuesday and although Ms Haley has narrowed the gap, polling still suggests the former president has a substantial lead.
Since Ms Haley's popularity has risen in the state, Mr Trump has ramped up his attacks on his former UN Ambassador, who was born in South Carolina to immigrant parents from India. Those born in the US are eligible for office.
In addition to spreading an article claiming Ms Haley cannot run for president, Mr Trump also referred to her by her birth name, Nimarata, calling her "Nikki 'Nimrada' Haley" on his social media platform Truth Social. Ms Haley's middle name is Nikki.
Asked about the post and article by CNN's Jake Tapper, Ms Haley said she was a "proud daughter of Bamberg, South Carolina".
"I love my sweet town and I'm proud to say I'm from there. So, that's the first question, we can throw that out the window," she said.
"I know that I am a threat. I know that's why he's doing that," she said, adding she would not get into "name-calling" with him.
When Mr Trump first shared an article questioning Ms Haley's eligibility for office last week, Laurence Tribe, a constitutional expert at Harvard Law School told NBC the "birther" claims were totally baseless.
"I can't imagine what Trump hopes to gain by those claims unless it's to play the race card against the former governor and UN ambassador as a woman of colour - and to draw on the wellsprings of anti-immigrant prejudice by reminding everyone that Haley's parents weren't citizens when she was born in the USA," he added.
Earlier this week, when asked by Fox News host Brian Kilmeade if the Republican Party was racist, Ms Haley responded with a broader point: "We're not a racist country, Brian. We've never been a racist country," she said.
Ms Haley said she had experienced racism growing up, but said things had improved. "Are we perfect? No," she added. "But our goal is to always make sure we try and be more perfect every day that we can."
Her comments provoked a backlash from some critics who accused her of ignoring America's history of slavery and segregation as well as racism and discrimination today.
Defending the comments, a spokesperson for Ms Haley said there was a difference in recognising that racism exists and calling the US a "racist country".
Despite finishing in third place in last week's Iowa caucuses, behind Mr Trump and Florida Governor Ron DeSantis, Ms Haley has attempted to portray the race for the Republican presidential nomination as a two-horse race between her and the former president.
Experts say she needs a strong performance in New Hampshire to prove she is a genuine contender when the campaign moves on.
