British Ambassador to the United States Peter Mandelson was sacked on Thursday following revelations about his friendship with convicted sex trafficker Jeffrey Epstein.

The recently released Epstein's 50th "birthday book" contains a letter from Mandelson, who called Epstein his "best pal."

Epstein, who had extensive connections with U.S. political and business elites, was arrested on sex crime charges and died in prison in August 2019. His death was officially ruled a suicide.

Details revealed by the media show that Mandelson told Epstein to "fight for early release" in their email correspondence when Epstein faced charges over soliciting a minor.

"I can still barely understand it. It just could not happen in Britain," Mandelson wrote to Epstein in his email.

"The emails show that the depth and extent of Peter Mandelson's relationship with Jeffrey Epstein is materially different from that known at the time of his appointment," said Britain's Foreign, Commonwealth and Development Office in a statement.

"In particular, Peter Mandelson's suggestion that Jeffrey Epstein's first conviction was wrongful and should be challenged is new information. In light of that, and mindful of the victims of Epstein's crimes, he has been withdrawn as Ambassador with immediate effect," it added.