Donald Trump plunged his quest for America's next top diplomat back into the spotlight by confirming that one frontrunner, outspoken former New York mayor Rudy Giuliani, will not join his cabinet.

Giuliani had made no secret of his desire for the job, but came under media scrutiny over business dealings that could pose conflicts of interest.

He was one of Trump's most ardent supporters in the bitterly divisive election but others were alarmed about the prospect of the 72-year-old known for abrasive rhetoric heading up the largest diplomatic mission in the world.

Observers in the United States and around the world have been on tenterhooks over who the incoming Republican will pick as they wait to see whether Trump will make good on threats to rip up treaties and free trade agreements.

With the decision expected next week, the president-elect announced Friday that Giuliani had removed his name from contention as far back as November 29.

"Rudy would have been an outstanding member of the cabinet in several roles, but I fully respect and understand his reasons for remaining in the private sector," Trump said in a statement.

Giuliani, a former federal prosecutor, earned the moniker "America's Mayor" for his leadership of New York in the wake of the September 11 attacks.

"This is not about me; it is about what is best for the country and the new administration," he said in a statement released by Trump's team, confirming that he would continue to work in his law and consulting firms.

The New York Times reported that Rex Tillerson, chief executive of Exxon Mobil, was now the leading candidate to become secretary of state. Tillerson met Trump in New York on Tuesday.

- New picks next week -

Former Republican presidential nominee Mitt Romney, a fierce critic of Trump during the campaign, is thought to remain in the running.

But the Times said Trump had "indicated to several people" that the former Massachusetts governor was now unlikely to be named.

In an interview with Fox News, Giuliani followed other ardent Trump loyalists in counseling against Romney, complaining that he "went just a little too far" in savaging Trump during the campaign season. 

"You can make friends and make up, but I would not see him as a candidate for the cabinet," Giuliani told Fox.

Trump's appointments so far include four billionaires and three generals in a super-rich, conservative and largely white inner circle set to run the United States from January 20.

Many incoming cabinet members have railed against the worker protections and environmental and corporate regulations enacted by President Barack Obama.

Trump told a victory rally in Michigan that "phenomenal" new names would be announced next week, but declined to give specifics.

The stop in Grand Rapids was the fifth campaign-style event since the November 8 election as he soaks up adulation from supporters in key states that helped secure his electoral win over Democrat Hillary Clinton.

The president-elect defends his picks as "some of the most successful people in the world" but when his choice for education secretary, billionaire Betsy DeVos, took the stage in Michigan, she was heckled by some protesters.

A number of protesters were forcibly removed from the floor at different points during the evening. "Where do these people come from? Unbelievable," said Trump as the crowd responded with chants of "U-S-A! U-S-A!"

- Oil refineries -

He used the rally to name Michigan resident and Australian-born Dow Chemical executive Andrew Liveris as head of a national manufacturing council. 

Liveris said his company was going to invest in a new research and development center in Michigan that would create hundreds of jobs -- with job creation one of Trump's key promises.

The president-elect also rehashed his complaints about a Boeing contract to build  two new Air Force One jets, which he claims has escalated to $4 billion. 

"I'm not paying $4 billion for an airplane," he told the crowd.

At a rally in Louisiana earlier on Friday, the president-elect said he wanted to see more oil refineries built in the United States, and pledged to do away with "job-killing restrictions" suppressing the energy sector.

He also delivered a veiled warning to America's rivals around the world, stating he would be prepared to boost US military production to keep pace with countries like China, which is rapidly modernizing its armed forces.

"We're going to have the strongest military in the world, the most updated military in the world. And there has rarely been a time where we have needed it like this," he told the crowd in Michigan.

Source: AFP