"You're welcome; we'd love to have you work in the fields with us," Mr Sasse said.

"Work in the fields!" Senator, I'm a house n----," Maher responded, adding that he was joking.

The senator smiled at the comment and the audience laughed and applauded.

However, it sparked outrage on social media, with many drawing comparisons with comedian Kathy Griffin, who has been vilified this week for staging a photoshoot with Donald Trump's severed head.

Deray Mckesson, an activist for Black Lives Matter, said: “But really, @BillMaher has got to go. There are no explanations that make this acceptable.”

"Bill Maher must be fired immediately for his racism and belittling the struggle of millions of black Americans," tweeted Jack Posobiec, a pro-Trump media figure.