A threatening letter, accompanied by a photo of an ISIS extremist, was sent to a police station in Sydney. Photo: Screenshot

Counter-terrorism officials are investigating a letter sent to a police station in Sydney, Australia, issuing threats against Jewish schools and others, the U.K.’S Daily Mail reported on Tuesday.

Police headquarters confirmed that the Holroyd Police Station in Merrylands received the note, which included threats to kill Jews, police and non-Muslims, along with an accompanying photograph of an ISIS terrorist with an array of severed heads. Radio 2GB broadcaster Ray Hadley revealed details of the letter on his show Tuesday morning.

“The letter contains threats of violence against non-Muslims. In particular, it targets Jewish schools and New South Wales police stations,” Hardley said. “It warns that thousands will die.”

The broadcaster said police are treating the letter as a serious threat, and are trying to trace its origins.