One year into the job, Nikki Haley stands out as the star of United States (US) President Donald Trump's administration, and diplomats say the United Nations (UN) ambassador is directing some of that star power into a likely White House bid.

Speculation about Haley's presidential ambitious has picked up since she defended Trump's decision to recognise Jerusalem as Israel's capital, staring down friends and foes alike at the world body.

The 45-year-old Republican resorted to a veto to block criticism from the UN Security Council and threatened reprisals against those who voted against Washington at the General Assembly.

The clash gave UN ambassadors a reality check: Haley, they say, is a politician, not a diplomat, and at the UN, she is playing to a domestic audience.

“She is not trying to win votes at the General Assembly. She is trying to win votes for 2020 or 2024,” a council diplomat said. “She is clearly using this position to run for something, that's obvious.”

The former South Carolina governor arrived at the UN last year, promising a “new day” under Trump's America First policy and vowing to “take names” of countries that don't toe the line.

Seen at the outset as a foreign policy lightweight, Haley was quickly taken seriously because of her close ties to the unpredictable Trump.

Over the past year, she has pushed through three new sets of sanctions against North Korea, bringing China and Russia on side to tackle what Trump sees as his administration's number one security threat.

Those sanctions won the unanimous backing of the council, where finding common ground with Haley is testing diplomatic skills.

The daughter of Indian immigrants, Haley is hawkish on Iran, fiercely pro-Israel and a strong advocate of cost-cutting at the UN.

Signature issues

That those three signature issues play well with the US Republican voter base is not lost on most diplomats.

“What matters above all are perceptions internally, in the US,” said another council diplomat, who like many declined to be quoted.

Haley was among the first administration officials to take a hard line on Russia, declaring that sanctions over Crimea would remain in place until Moscow gave the territory back to Ukraine.

Ukrainian Ambassador Volodymyr Yelchenko, who just wrapped up a two-year stint at the Security Council, says Haley is doing an “excellent job.”

“She may be less diplomatic sometimes than some could expect, but this is more an asset than a shortcoming,” he said.

For months, Haley had been tipped as a possible replacement to US Secretary of State Rex Tillerson, whom she has upstaged with her media appearances and statements that at times appear to break new ground.

In October, she put that speculation to rest, telling reporters that she wasn't interested.

“I would not take it,” Haley told reporters on a trip to the Democratic Republic of Congo. “I want to be where I'm most effective.”

She is seen as a possible vice president to Mike Pence, should he take over the presidency.

Author Michael Wolff, whose book “Fire and Fury: Inside the Trump White House” has become a national sensation, claims Haley has set her sights higher and is eyeing the presidency.

According to published excerpts, Haley began positioning herself as Trump's heir after concluding in October that he was a one-term president.

Wolff quoted a senior White House staffer who described her “as ambitious as Lucifer” and another who offered the view that while being groomed by Trump, “she is so much smarter than him.”

Haley has brushed aside questions about her political ambitions, saying she is focused on the job at hand as she remains firmly in the limelight as the UN's most-watched ambassador.