US Attorney General William Barr, who recently opposed Donald Trump on allegations over the November 3 elections being fraudulent, has resigned.

His deputy, Jeff Rosen, was appointed by the outgoing President as Acting Attorney General.

“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,” Trump wrote on twitter on Monday night.

“Deputy Attorney General Jeff Rosen, an outstanding person, will become Acting Attorney General. Highly respected Richard Donoghue will be taking over the duties of Deputy Attorney General. Thank you to all,” he said in another tweet, with the two-page resignation letter of Barr.

Barr in his letter said, “As discussed, I will spend the next week wrapping up a few remaining matters important to the administration, and depart on December 23.”

“I am greatly honored that you called on me to serve your administration and the American people once again as Attorney General. I am proud to have played a role in the many successes and unprecedented achievements you have delivered for the American people. Your record is all the more historic because you accomplished it in the face of relentless implacable resistance,” the letter added.

Democratic Congressman David Cicilline alleged that Barr aided and abetted Trump's attacks on the US elections.

“He has done incalculable damage to our democracy. He will not be missed,” Cicilline tweeted.

Congressman Adam Schiff, Chairman of the House Armed Services Committee, alleged that Barr lied to cover for Trump.

“Launched political investigations. Subverted justice and the rule of law. And violently cracked down on protesters. So good riddance. Now, the work of restoring a credible and independent justice system must begin,” he said.