Popular talk show host David Letterman received a death threat on an extremist networking site frequented by al Qaeda, a U.S. intelligence monitoring group said on Wednesday.

A Muslim militant, who identified himself as Umar al-Basrawi, urged Muslim followers to "cut the tongue" of the late night host, after the writer was offended by a joke Letterman made about the death of a leading member of al Qaeda killed in an airstrike in Pakistan, said The Site Monitoring Service, a private intelligence organization that watches online activity.

The threat was posted on the "Shumuka al-Islam" forum, a popular Internet destination reportedly used by al Qaeda members when they were under America's radar following the September 11 attacks.

"It's a clearing house for al Qaida material, it gets the most al Qaida supporters," Adam Raisman, an analyst at SITE told Entertainment Weekly.

The writer who posted the message was upset by a segment on the "Late Show" which showed Letterman drawing his finger across his neck when talking about the death of senior al-Qaida member Ilyas Kashmiri.

"Is there not among you a Sayyid Nosair al-Mairi ... to cut the tongue of this lowly Jew and shut it forever?" Al-Basrawi wrote, according to a translation by SITE. Letterman is not Jewish.

The writer was referring to El Sayyid Nosair, who was convicted in the 1990 killing of Jewish Defense League founder, Meir Kahane.

"He showed his evil nature and deep hatred for Islam and Muslims, and said that Ilyas Kashmiri was killed and he joined bin Laden. We ask Allah to paralyze his tongue and grant the sincere monotheists his neck," Al-Basrawi wrote.

Neither CBS nor a Letterman spokesman would comment on the threat.

The FBI is looking into the threats, a spokesman for the FBI told the Associated Press.

"We take every potential threat seriously," he said.