US President Donald Trump talks with UN Ambassador Nikki Haley in the Oval Office of the White House, Oct. 9, 2018. Photo: Reuters / Jonathan Ernst.

The US ambassador to the United Nations, Nikki Haley, announced on Tuesday she is resigning, and immediately denied she was preparing to challenge President Donald Trump in the 2020 presidential election.

Sitting beside Trump in the Oval Office, Haley said her 18-month stint at the United Nations had been “an honor of a lifetime” and said she would stay on until the end of the year.

Haley, 46, is the latest in a long line of high-profile departures from the administration, such as former Secretary of State Rex Tillerson, who was fired in March, and Steve Bannon, Trump’s chief strategist, who left in August 2017.

Describing her time at the United Nations as “fantastic” and “incredible,” Trump said he had accepted Haley‘s resignation and would name her successor within two or three weeks.

A former governor of South Carolina who is the daughter of Indian immigrants, Haley is a rising star in the Republican Party and is often mentioned as a possible candidate for the 2020 presidential elections.

But she said on Tuesday she would not be running and would campaign for Trump. “No, I am not running for 2020,” she said.

Echoing previous statements from Trump, Haley said the United States under his presidency is now respected around the world.

“Now the United States is respected. Countries may not like what we do, but they respect what we do. They know that if we say we’re going to do something, we follow it through,” she said.

Haley has been the face of Trump’s “America First” policy at the United Nations, steering the US withdrawal from several UN programs and ardently defending his hard-line policies against Iran and North Korea over their nuclear programs.

“She has done an incredible job. She is a fantastic person, very importantly, but she also is somebody that gets it,” Trump said on Tuesday. She told Trump around six months ago that she was thinking of quitting by the end this year “to take a little time off,” he said.

“She’s done a fantastic job and we’ve done a fantastic job together. We’ve solved a lot of problems and we’re in the process of solving a lot of problems,” he said.

Haley discussed her resignation with Trump last week when she visited him at the White House, Axios news site reported.

Her UN counterparts described her as charming and yet very tough. She saw herself as a fighter.

“I don’t see (my role) as pushing an ‘America First’ policy, I see it as defending America because every day I feel like I put body armor on. I just don’t know who I’m fighting that day,” Haley told Reuters earlier this year.