Twitter on Monday permanently suspended the account of Paul Nehlen, an alt-right politician in the United States, for tweeting a racist image of actor Meghan Markle. The self-declared white supremacist had shared a photoshopped image of Markle with Britain’s Prince Harry, her fiancé, with an image of the Cheddar Man – a dark-skinned man believed to be the first modern Briton – superimposed on her face.

The tweet posted on Friday showed a photoshopped Markle standing beside Prince Harry with the caption, “Honey does this tie make my face look pale?” After Twitter suspended his account, Nehlen called it an effort to “suppress right-wing political speech” and “the epitome of interfering with a federal election”, The Washington Post reported.

“These are unprecedented, brazen acts of censorship by a corporate monopoly that controls a primary channel of public communication,” the Republican said. “It has severely compromised the integrity of our election processes, and Congress needs to hold public hearings and conduct a full investigation into these matters without delay.”

Nehlen’s tweet may have been prompted by the recent discovery that, as initially believed, early British inhabitants did not have pale skin. DNA evidence showed that Cheddar Man had brown hair, blue eyes and “dark to black skin”. He lived 10,000 years ago, and his skeleton was discovered in 1903 in a cave in Cheddar Gorge in Somerset, England. After analysing his skeleton further and some facial reconstruction, scientists concluded that his ancestors arrived in Britain from West Asia after leaving Africa.

On Sunday, Nehlen tried to defend his tweet after much criticism by targeting the Cheddar Man research. “A deliberately inflammatory article [that I’d argue is pure junk science] was published indicating Brits, and by extension Americans, came from this Cheddar Man character,” he wrote on Facebook. “In response, I lampooned the article.”

Nehlen is currently running against US House of Representatives Speaker Paul Ryan for the congressional primaries in Wisconsin. A Twitter spokesperson confirmed that the social media company had permanently suspended Nehlen’s account for “repeated violations of our terms of service”.

Corrections and clarifications: An earlier version of this story erroneously said Paul Nehlen was a Republican Party leader.