The leader of the so-called alt-right movement, a movement accused of racism and anti-Semitism, has been asked to leave a conservative event.
Richard Spencer's removal from the Conservative Political Action Conference (CPAC) came as one of the organisers attacked his views.
Dan Schneider called the alt-right "a sinister organisation that is trying to worm its way into our ranks".
"They are anti-Semites. They are racists," he said.
"They are not an extension of conservatism. They are nothing but garden-variety, left-wing fascists," Mr Schneider continued in Thursday's speech, titled The Alt Right Ain't Right At All.
As he was speaking, Mr Spencer got up from his seat and left the conference hall.
"They are not a part of us," said Mr Schneider, of the American Conservative Union.
Afterwards, during a nearly hour-long briefing with reporters in the hallway, Mr Spencer said he had paid money to attend the annual gathering outside Washington, and that his anti-minority views are "clearly resonating with people".
He condemned Mr Schneider's speech as "totally stupid", and in a tweet paraphrased a Mahatma Gandhi quote: "First they ignore you. Then they laugh at you. Then they fight you. Then you win."
As he was talking to reporters, a security guard approached to escort him from the conference.
Shortly after the election of Donald Trump, who Mr Spencer supports, he came to Washington where he led an alt-right gathering in making Nazi salutes while chanting: "Heil Trump!"
He was also punched in the face during protests that shook the US capital in the days after Mr Trump's inauguration as US president.