US Attorney General William Barr, one of Donald Trump's staunchest allies, is stepping down before Christmas, the president has announced.

Mr Barr's term was due to end on 20 January, when Mr Trump leaves office.

Tensions between the two flared after Mr Barr said there was no evidence of widespread fraud in November's vote.

US Attorney General William Barr will leave the role 'before 25 December', President Trump announces https://t.co/Vl7HC54kER

— BBC Breaking News (@BBCBreaking) December 14, 2020

He was criticised by Mr Trump for not publicly disclosing during the election campaign that the justice department was investigating Joe Biden's son.

Mr Trump tweeted Mr Barr's resignation letter saying: "Our relationship has been a very good one, he has done an outstanding job!"

Mr Barr's letter to the president began by saying he "appreciated the opportunity to update" the president on the Department of Justice's (DOJ) review of voter fraud allegations in the recent election and "how these allegations will continue to be pursued".

He did not give more details about the review, and praised Mr Trump's achievements in office before ending the letter by saying he would depart from his position on 23 December.

Just had a very nice meeting with Attorney General Bill Barr at the White House. Our relationship has been a very good one, he has done an outstanding job! As per letter, Bill will be leaving just before Christmas to spend the holidays with his family...

— Donald J. Trump (@realDonaldTrump) December 14, 2020

Deputy Attorney General Jeff Rosen will serve as acting attorney general, Mr Trump said.