Image copyright Reuters Image caption Nick Ayers (left) had been rumoured to be Mr Trump's pick to replace current chief of staff John Kelly (right)

Speculation is mounting over who will be US President Donald Trump's new chief of staff after the man believed to be the top candidate said he too was leaving the government.

Nick Ayers, chief of staff to the vice-president, will reportedly return to his home state of Georgia.

The 36-year-old was seen as Mr Trump's main choice to replace Gen John Kelly, who will depart by the year's end.

But the president appeared to dismiss the idea he had wanted Mr Ayers.

"I am in the process of interviewing some really great people for the position of White House Chief of Staff," he said in a tweet.

"Fake News has been saying with certainty it was Nick Ayers, a spectacular person who will always be with our #MAGA [Make America Great Again] agenda. I will be making a decision soon!"

Who's on the list?

Exactly who is on the list of interviewees is a source of debate among US media outlets.

According to the Washington Post, Republican congressman Mark Meadows, a leader of the ultraconservative House Freedom Caucus, and Mick Mulvaney, the White House's budget director, are in contention.

On Monday, Mr Meadows told Politico that "serving as chief of staff would be an incredible honour". Pundits interpreted the statement as an indication that he may be interested in taking on the role.

Former New Jersey Governor Chris Christie is also reportedly on Mr Trump's shortlist. A source in the Trump administration told CNN that he considered a "strong option" to restore "a functioning White House".

Mr Christie had led the transition team when Mr Trump was first elected, but was abruptly removed three days after Mr Trump's victory following widely reported clashes with Jared Kushner, the US president's son-in-law.

CNN added Treasury Secretary Steve Mnuchin to the list of possibilities, although this was played down by a source close to the former investment banker.

But exactly who will be brave enough to take on the role remains to be seen.

Chris Whipple, author of The Gatekeepers: How the White House chiefs of staff define every presidency, told Politico: "You really do have to wonder why anybody would want to be Donald Trump's White House chief of staff given that so far it's been mission impossible."

A house of chaos and uncertainty

Analysis by Anthony Zurcher, BBC News

A presidential chief of staff is one of the most prestigious jobs in Washington.

He or she holds the (metaphorical) keys to the White House. While the president has the final say in matters, the chief of staff wields incredible informal power and influence.

There's no telling what kind of behind-the-scenes machinations led Nick Ayers to pull his name out of the running for the job, but for an up-and-coming 36-year-old political player to pass on the opportunity is remarkable.

This isn't the first time a key administration job has opened up without a guaranteed replacement waiting in the wings. It suggests there's plenty of truth to reports of chaos and uncertainty within the Trump White House.

Now the search is on for someone to fill John Kelly's position. In normal times, candidates would be queuing up for the opportunity.

With the president under investigation, the party reeling from mid-term election losses and the potential for economic turmoil ahead, however, these are not normal times.

Why is Kelly leaving?

Earlier this year, Gen Kelly, who took over from Reince Priebus in July 2017, was forced to deny he had called Mr Trump an "idiot" after the quote was included in a book about Mr Trump by the veteran investigative journalist Bob Woodward.

Gen Kelly is said to have used the description repeatedly and also allegedly said that "it's pointless to try to convince him of anything".

Media playback is unsupported on your device Media caption What Mr Kelly said in October 2017: 'I was not brought in to control Trump'

Mr Ayers name emerged as a possible replacement last month as reports of Gen Kelly's deteriorating relationship with the president began to circulate.

But on Sunday, he made it clear he would not be taking on the role in a tweet saying he was resigning from the White House.

According to Politico, Mr Ayers' friends have suggested he wants to run for public office in his home state, Georgia.

However, CNN said two sources said First Lady Melania Trump and "some other senior staff" had intervened to block Mr Ayers.