A billionaire Republican mega-donor, credited with helping propel Donald Trump to power, announced on Thursday he was selling his stake in Breitbart News after being accused of fuelling the rise of the alt-Right.

In a memo sent to employees of his hedge fund Renaissance Technologies, Robert Mercer denied that he was a white supremacist and dissociated himself from the views of Milo Yiannopolous, a Rightwing provocateur.

“I was mistaken to have supported him, and for several weeks have been in the process of severing all ties with him,” wrote Mr Mercer, according to Buzzfeed News.

Mr Mercer’s deep pockets and stake in Breitbart News, the conservative news service, made him a key player in last year’s election. His close relationship with Steve Bannon, who served as Mr Trump’s chief strategist at the White House, also meant the campaign had access to his data analytics firm, Cambridge Analytica.

However, he has come under increasing pressure for views expressed by contributors and staff at the news site.