In the surprise announcement, she said she will leave at the end of the year.

She said that she did not know as yet what she will be doing next, but ruled out a run for president in 2020 saying she would campaign for Trump.

After eight years of public service -- two as a governor and two as UN ambassador - she said that she wanted a change after the stressful tenures and that government officials should limit their terms in office so that there are new people coming in.

Trump praised her for her role at the UN saying that she was respected by leaders and diplomats at the UN and that the US is more respected.

He called her a "special friend" and said he hoped to see her back in some capacity in the administration or politics.

The daughter of Sikh immigrants from Amritsar district, Haley had a meteoric rise in Republican politics and was the megaphone of President Donald Trump's aggressive global policy at the UN often using harsh rhetoric at opponents.

She was the first woman and non-white to be elected governor of South Carolina before she was appointed the UN ambassador -- a cabinet post in the US.

Haley is very popular among Republicans. But she was despised by Democrats -- especially Indian Americans -- who hold that non-white persons should not be in the Republican Party and hold a high government office in Republican Administration.

The resignation of the highest profile woman in Trump's cabinet less than a month before the mid-term elections roils the political situation just after widespread protests by women's groups and polarisation over the nomination of Brett Kavanaugh, who was accused of sexual harassment, to the Supreme Court.

Her main achievement was getting China and Russia to stringently adhere to Security Council sanctions on North Korea, which ultimately led to its Kim Jong Un agreeing to negotiate denuclearisation with the US.

Trump praised her role on North Korea, which led to his diplomatic coup.

She also backed the moving the US embassy to Jerusalem, which led to the virtual isolation of Washington at the UN, with even allies abandoning it.

She also backed cutting US aid to the UN agency for Palestinians.

In addition, she was behind the US pulling out of the UN Human Rights Council because, she said, it included several human rights violators.

Despite promoting the Trump's policies, she also had differences with him, pursuing a far more aggressive policy towards Russia than Trump does.

While Rex Tillerson was the Secretary of State, she had a higher profile, which dimmed somewhat after Michael Pompeo took the job and assumed a more public role.

She was also hemmed in by National Security Adviser John Bolton, a former US Permanent Representative, with his own foreign policy agenda that was sometimes at odd with Pompeo on North Korea and Russia.

Haley had been a critic of Trump during the campaign for Republican Party nomination for president in 2016 and supported Marco Rubio. But after Trump won the nomination, she supported for him.

She acknowledged that she had differences with Trump while at the UN but could air her views with him.

In an op-ed in The Washington Post, she wrote, "I don't agree with the president on everything. When there is disagreement, there is a right way and a wrong way to address it. I pick up the phone and call him or meet with him in person."

After her departure, among the high-ranking Trump administration officials are Ajit Pai, the Federal Communications Commission Chairperson, and Seema Verma, the Administrator of the Centers for Medicare and Medicaid Services.

Neither are at cabinet level.