US President Donald Trump has accepted the surprise resignation of UN Ambassador Nikki Haley.
He told reporters in the Oval Office alongside Mrs Haley that she would be leaving the post at the end of the year after doing "an incredible job".
The 46-year-old former South Carolina governor - who is one of the few women in the Trump cabinet - gave no reason for her exit after two years.
But she dismissed speculation she was planning to run for president in 2020.
Mrs Haley told journalists she would be campaigning for "this one", pointing to Mr Trump.
"I don't have anything set on where I'm going to go," she said.
"It's been eight years of intense time, and I'm a believer in term limits.
"I think you have to be selfless enough to know when you step aside and allow someone else do the job."
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Analysis by Nick Bryant, BBC UN correspondent
Through the revolving door of the Trump administration goes another high-level departure: UN ambassador Nikki Haley, by far the most high-profile woman in the cabinet, and an internationalist who's done much to protect the United Nations from Donald Trump's anti-globalist wrecking ball.
She was a strident critic of Russia and Syria at the UN, and also fiercely critical of what she claimed was the global body's anti-Israel's bias. She supported shutting off US funding for the UN's Palestinian refugee agency and revelled in defending the Trump administration's decision to move its embassy in Israel from Tel Aviv to Jerusalem in the face of an acid show of international criticism. She was also instrumental in pressuring China to support a tough sanctions regime against North Korea.
Sometimes, however, her style grated with colleagues. Her aggressive and repeated warnings about compiling a list of countries that didn't back the United States irritated even close allies. Yet it's often said that the UN's biggest peacekeeping mission is directed against the Trump White House, and Nikki Haley was seen as a valuable ally.
A former governor of South Carolina, she's a talented retail politician who's widely spoken of as a future female US president. Though she has ruled out challenging Donald Trump in 2020, we have not heard the last of Nikki Haley.
Mr Trump said Mrs Haley had told him six months ago she wanted to take some time off.
The president said she "has been very special to me, she has done an incredible job, she is a fantastic person, very importantly, but she is also somebody that gets it".
"Hopefully you'll be coming back at some point, right," Mr Trump said. "Maybe a different capacity, you can have your pick." Mrs Haley laughed.
Mr Trump said he would be naming her replacement in the next two to three weeks.
Who is Nikki Haley?
- Born Nimrata Randhawa to Indian immigrant parents, she was raised as a Sikh in Bamberg, South Carolina, later converting to Christianity
- Her first job as a 13-year-old was bookkeeping for her family's clothing store
- In 2010, she became South Carolina's first female and first minority governor - and youngest governor in the US - and was re-elected in 2014
- She received nationwide praise for removing the Confederate flag from the state capitol after a mass shooting on black churchgoers in Charleston in 2015
- She did not initially endorse Mr Trump during the 2016 campaign, instead backing Florida Senator Marco Rubio
- Mrs Haley is married to Army National Guard Captain Michael Haley, and the couple have two teenage children Credit: The BBC