J.K Rowling has accused Nigel Farage of using Nazi-style propaganda in his EU referendum campaign.
In an article on her website published on Monday, the Harry Potter author said people should consider that "racists" are directing the 'Leave' campaign before deciding to back Brexit.
She warned both sides of the campaign wanted voters to be "frightened only by monsters of their choosing".
"The picture of Nigel Farage standing in front of a poster showing a winding line of Syrian refugees captioned 'Breaking Point' is, as countless people have already pointed out, an almost exact duplicate of propaganda used by the Nazis," she wrote.
The Ukip leader has been criticised by both sides of the referendum for the billboard. But Farage has accused David Cameron and other pro-EU MPs of unfairly linking the poster to the killing of Labour MP Jo Cox.
In her article, Rowling said the referendum campaigns had been "appealing to us through our universal need to make sense of the world by storytelling and that they have not been afraid to conjure monsters calculated to stir up our deepest fears".
She added: "I'm not an expert on much, but I do know how to create a monster."
In a few days' time, we'll have to decide which monsters we believe are real and which illusory J.K Rowling on Brexit
However the author, who is backing a 'Remain' vote, reserved her deepest criticism for the 'Leave' camp.
"It is dishonourable to suggest, as many have, that Leavers are all racists and bigots: they aren't and it is shameful to suggest that they are. Nevertheless, it is equally nonsensical to pretend that racists and bigots aren't flocking to the 'Leave' cause, or that they aren't, in some instances, directing it. For some of us, that fact alone is enough to give us pause," she said.
"I don't think the EU's perfect. Which human union couldn't use improvement? From friendships, marriages, families and workplaces, all the way up to political parties, governments and cultural economic unions, there will be flaws and disagreements. Because we're human."
Rowling also took aim at Republican presidential candidate Donald Trump - who is due to visit the UK this week - as a "fascist in all but name".
"His stubby fingers are currently within horrifyingly close reach of America's nuclear codes," she wrote.
"He has the temperament of an unstable nightclub bouncer, jeers at violence when it breaks out at his rallies and wears his disdain for women and minorities with pride. God help America. God help us all."
Vote Leave campaign chairman Michael Gove has said Farage's poster made him “shudder”.
George Osborne said it was “disgusting” and compared it to Nazi propaganda. Cameron said it was an “irresponsible” attempt to “frighten people”.
Farage has defended the billboard. "When I launched the poster there was no controversy at all,” the Ukip leader told LBC this morning.
"What we are seeing here is the prime minister and ‘Remain’ campaign trying to conflate the actions of one crazed individual with the motives of half of Britain who think we should get back control of our borders and do it sensibly and I think it’s quite wrong the way it’s being done."