"At the end of the year Nikki will be leaving", Trump told reporters, after praising the United Nations ambassador. Nevertheless, the announcement surprised many in the Trump administration.

She gave no reason for her departure after two years, though there is speculation she will return to government or politics at some point.

Instead of answering directly, he recounted how she has had to work on tough issues, such as Iran and North Korea.

"I think you have to be selfless enough to know when you step aside and allow someone else do the job".

"Nikki Haley has set a new standard for what American leadership at the United Nations should look like", Rep. Mark Meadows (R-N.C.) said in a tweet.

But she said in her resignation letter to Trump she would "surely not be a candidate for any office in 2020" and would support his re-election bid. Marco Rubio (R., Fla.).

Haley, who previously served as the governor of SC from 2010 to 2016, thanked Trump and said serving in his administration was "an honor of a lifetime".

"I don't have anything set on where I'm going to go", Haley said, adding that "it has been the honor of a lifetime" to serve as United Nations ambassador.

Trump said he would announce Haley's successor in the next two to three weeks, signalling that "many people" are interested in the job. Wolff, in his book, claims Haley has an eye on the presidency and Trump is seen to be grooming her for a national political future.

Tuesday's announcement prompted widespread praise of Haley's tenure from fellow Republicans, but some lawmakers expressed concerns about the timing.

If this was long-planned, it was apparently the best-kept secret in Trump's White House.

Citizens for Responsibility and Ethics in Washington filed the complaint against Haley, who has g earned high marks for navigating global affairs and the challenges of the Trump administration, on Monday.

On Monday, the federal watchdog group Citizens for Responsibility and Ethics in Washington (CREW) called for the State Department's inspector general to launch an ethics investigation into Haley, regarding seven free flights on private planes that Haley and her husband accepted from three SC businessmen in 2017.

In December 2017, she said that women who had accused Mr Trump of sexual assault "should be heard".

Haley's is the latest resignation in a turbulent White House, where Trump is already on his third national security adviser and second secretary of state before even the midterm elections.

News of Haley's departure broke Tuesday morning, Donald Trump accepting her resignation personally.

She wanted to see what was happening on the ground, travelling to Israel, South Sudan, the Democratic Republic of Congo and Latin America.