An associate professor who sparked widespread backlash after he tweeted "All I Want for Christmas is White Genocide" claimed on Monday that his critics -- some of whom were "violent racists" -- simply didn't get the joke.

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Drexel University administrators clearly thought George Ciccariello-Maher's tweet was no laughing matter. "The University is taking this situation very seriously. We contacted Ciccariello-Maher today to arrange a meeting to discuss this matter in detail," they said in a statement.

Ciccariello-Maher, who is white and an associate professor of politics at the Philadelphia university, fired back in a statement to The Philadelphia Inquirer. "While Drexel has been nothing but supportive in the past, this statement is worrying... I teach regularly on the history of genocidal practices like colonialism and slavery -genocides carried out by the very same kind of violent racists who are smearing me today."

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The controversy got the attention of white nationalist leader Richard Spencer, who tweeted, "Anyone at Drexel able to bring me to speak to the student body?"

The Drexel statement continued, "While the University recognizes the right of its faculty to freely express their thoughts and opinions in public debate, Professor Ciccariello-Maher's comments are utterly reprehensible, deeply disturbing, and do not in any way reflect the values of the University."

The associate professor, whose online biography claimed his academic specialties included "race and racism," said Drexel apparently didn't understand "the content or the context" of his tweets. The professor told The Associated Press he was mocking what he called the "imaginary concept" of white genocide, which he says was invented by white supremacists.

Ciccariello-Maher followed up his initial tweet by praising the "massacre" of whites in Haiti during the country's slave uprising and revolution more than two centuries ago.

Though his Twitter account is private, he is a prolific tweeter with more than 11,000 followers, and his weekend messages spread quickly online. He said he has received hundreds of death threats and claimed Drexel's statement "sends a chilling message."

The Associated Press contributed to this report.