Chief of Staff John Kelly to leave White House by year-end: US President Donald Trump

White House Chief of Staff John Kelly will step down by the end of this year, US President Donald Trump has said, confirming that he will announce a replacement "over the next day or two".

The 68-year-old retired Marine Corps general has been President Trump's Chief of Staff since July 31, 2017. In the first seven months of the Trump administration, Kelly was the secretary of Homeland Security. "John Kelly will be leaving  I don't know if I can say 'retiring'. But, he's a great guy. John Kelly will be leaving at the end of the year," Trump told reporters at the White House on Saturday.

"We will be announcing who will be taking John's place...I shall be announcing that over the next day or two. But, John will be leaving at the end of the year. He has been with me almost two years now," Trump said.

Nick Ayers, the 36-year-old chief of staff to the vice-president Mike Pence, is Kelly's likely successor.  

There were reports that the relationship between Trump and Kelly had deteriorated to such an extent that the two were no longer on speaking terms.

Kelly, who was brought in by Trump after he fired Reince Priebus, has been instrumental in bringing in a sense of discipline inside the White House.

Kelly was one of the several generals appointed by Trump to key roles, including defense secretary Jim Mattis, and former national security advisers Michael Flynn and HR McMaster.

According to a report in 'The Wall Street Journal', the relationship between Kelly and Trump had completely broken down, leading the president to tell an associate to "stop calling John" and to instead "call Nick, he's my guy".

Veteran journalist Bob Woodward wrote in his bestselling book 'Fear' that Kelly called Trump an "idiot" at the head of a "Crazytown" administration.

Kelly, however, denied such reports and stayed in post.

In France in November for events marking the 100th anniversary of the end of the first world war, Kelly visited an American cemetery outside Paris while Trump remained in the city, the White House insisting rain made a presidential visit impractical.

Kelly's exit from the White House is the latest in a series of reshuffles in the Trump administration.

On Friday, Trump said he will nominate William Barr his attorney general, replacing Matthew Whitaker who was named acting attorney general only a month ago. Whitaker replaced Jeff Sessions in the top Justice Department post.

Sessions was fired after months of being attacked and ridiculed by the president on November 7.

Trump appointed State Department spokeswoman Heather Nauert as the US' next ambassador to the UN, replacing Indian-origin Nikki Haley who said in October that she would step down at the end of the year.

McMaster was replaced on March 22 with John Bolton as the national security adviser.

Scott Pruitt, the Environmental Protection Agency chief quit on July 5.

Former secretary of state Rex Tillerson was fired by Trump on March 13 after rifts between them. On Friday, Trump tweeted that Tillerson was "dumb as a rock" and "lazy as hell".

James Comey, the FBI director, who led the Russia probe before Mueller, was fired by Trump in May last year.

Michael Flynn resigned in February last year as Trump's national security adviser.

Earlier in the day, Trump nominated General Mark Milley as his next Chairman of the Joint Chiefs of Staff, the nation's top military advisor.

If confirmed by the Senate, Gen Milley would replace General Joe Dunford who is scheduled to retire next summer. Milley currently is Chief of Staff of the Army.

Trump described Gen Milley as a "great gentleman and a great patriot".