(Image source from: ABC News - Go.com)

An Indian-American Nikki Haley has resigned as the United States ambassador to the United Nations on Tuesday, according to several reports in the U.S. media.

A senior State Department official said Haley told her staff this morning.

The 45-year-old Haley is the first ever Indian-American appointed to a Cabinet-level position by any president.

The stepping down of Haley has left White House with one less moderate Republican voice on Trump cabinet's foreign policy team.

Haley, a former governor of South Carolina, had been an early and recurrent critic of Trump, attracting frequent admiration.

Haley was born in South Carolina to an Indian-American Sikh family. She earned international attention for speaking out against the Confederate battle flag in the aftermath of the 2015 massacre at a black church in Charleston.

According to Michael Wolff's book Fire and Fury: Inside the Trump White House, Haley is harboring presidential drives and many in president Donald Trump's inner circle fear that she could be the heir to the presidency. 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.

Haley - "as ambitious as Lucifer", in the characterization of one member of the senior staff - had concluded that Trump's tenure would last, at best, a single term and that she, with requisite submission, could be his heir apparent, Wolff writes.

"I said 'I am a policy girl, I want to be part of the decision-making process,'" she told CNN in a 2017 interview, recalling the conversation with Trump. "He said, 'done.' And I said, 'I don't want to be a wallflower or a talking head. I want to be able to speak my mind.' He said, 'That is why I asked you to do this.' In all honesty, I didn't think they were going to take me up on everything I asked for. And they gave me all that. So how do you turn that down?"

Throughout her over a year-and-a-half on the job, she has recurrently spoken her mind, whether it's going further on human rights than numerous of her administration colleagues or censuring racism at home.

-Sowmya Sangam