Former general joins a long list of Trump aides who have either quit or been sacked by the US leader.

White House Chief of Staff John Kelly will leave his post at the end of the year, United States President Donald Trump has announced.

An announcement about Kelly’s replacement was expected in the coming days, the president told reporters on Saturday as he departed the White House for the Army-Navy football game in Philadelphia.

“John Kelly will be leaving – I don’t know if I can say retiring – but he’s a great guy,” Trump told reporters.

“John Kelly will be leaving at the end of the year. We’ll be announcing who will be taking John’s place – it might be on an interim basis. I’ll be announcing that over the next day or two, but John will be leaving at the end of the year. … I appreciate his service very much.”

Nick Ayers, Vice President Mike Pence’s chief of staff, is Trump’s top choice to replace Kelly, and the two have held discussions for months about the job, a White House official told the Associated Press news agency.

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Trump and Ayers were working out specific terms under which Ayers would fill the role and the time commitment he would make, the official said.

Trump wants his next chief of staff to agree to hold the job through the 2020 election. Ayers had long planned to leave the administration at the end of the year. The official spoke to the AP on the condition of anonymity to discuss sensitive personnel matters.

The announcement comes a day after Trump named his picks for attorney general and ambassador to the United Nations, and two senior aides shifted from the White House to Trump’s campaign.

Kelly had been credited with imposing order on a chaotic West Wing after his arrival in June 2017 from his post as homeland security secretary. But his iron first also alienated some longtime Trump allies, and he grew increasingly isolated, with a gradually diminished role.

Known through the West Wing as “the chief” or “the general”, the retired Marine Corps four-star general was tapped by Trump via tweet to try to normalise a White House riven by infighting and competing power bases.

White House aides say Trump has developed confidence in Ayers, in part by watching the effectiveness of Pence’s largely independent political operation.

Ayers, 36, would be the youngest chief of staff since 34-year-old Hamilton Jordan served under Jimmy Carter. Kelly is 68.

Trump on Friday announced that he would nominate William Barr, who served as attorney general under President George HW Bush, to the same role in his administration.

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He fills the slot vacated by former Alabama Senator Jeff Sessions, who was jettisoned by Trump over lingering resentments for stepping aside from overseeing special counsel Robert Mueller’s investigation.

Trump also said that State Department spokeswoman Heather Nauert was his pick to replace Nikki Haley as the next US ambassador to the UN.

Earlier on Saturday, the president announced that he wanted Army Chief of Staff General Mark Milley as the next chairman of Joint Chiefs of Staff.

Among the other changes, two veterans of Trump’s 2016 campaign – White House political director Bill Stepien and Justin Clark, the director of the office of public liaison – are leaving the administration to work on his re-election effort.

Trump had discussed replacing Kelly on multiple occasions, including following the negative publicity surrounding his handling of domestic violence accusations against then-White House staff secretary Rob Porter.

Kelly, who had threatened to quit on several occasions, told friends he would be happy if he lasted until his first anniversary: July 28.