A website forum frequently utilized to spread Al-Qaeda dispatches has posted an assassination threat against David Letterman.

According to the SITE Intelligence Group, a private company that tracks extremist websites, a commenter called on Muslims to kill the CBS late-night host after taking offense at a joke made on the program. A poster calling himself Umar al-Basrawi wrote: “Is there not amongst you a Sayyid Nosair al-Masri (may Allah release him) to cut the tongue of this lowly Jew and shut it forever. Just as Sayyid (may Allah release him) did with the Jew Kahane.” Sayyid Nosair al-Masri was tried for the murder of Rabbi Meir Kahane in 1990.

SITE analyst Adam Raisman tells EW the threat was made on Shumukh-al-Islam, a site where messages from Al Qaeda frequently first appear online in the United States. “It’s a clearing house for Al-Qaeda material. It gets the most Al-Qaeda supporters,” he says.

Raisman ranked the threat as more worrisome than the “warning” posted against South Park creators Trey Parker and Matt Stone last year. “This was a more explicit threat,” he said. “It was direct and to the point.”

Letterman (who, by the way, is not Jewish) apparently mocked the death of accused terrorist leader Ilyas Kashmiri, who was killed by a U.S. airstrike in Pakistan in June. The poster said Letterman put a hand to his neck and demonstrated the “way of slaughter.” “He showed his evil nature and deep hatred for Islam and Muslims, and said that Ilyas Kashmiri was killed and he joined bin Laden,” he wrote. “We ask Allah to paralyze his tongue and grant the sincere monotheists his neck.” The news was first reported by Stars and Stripes.

Raisman’s group is currently trying to find out more information about the poster, who has more than 1,200 messages on the forum. He advises Letterman take “as much precaution as he would with an obsessed fan.” CBS had no comment.