Police are beefing up security at Pasadena High School on Thursday and Friday in response to an anonymous note threatening violence on the campus, school and public safety officials said.

The note did not specify who might commit violence and the writer appeared to be reporting the threat as secondhand information — “someone saying, ‘I heard this,’” Pasadena Unified spokesman Adam Wolfson told the Pasadena Sun.

A prerecorded telephone and email message went out to parents Wednesday night informing them about "an anonymous note" and a "threat of violence."

Investigators have found no information or evidence yet to substantiate the threat, but police and school officials “are giving special attention to the matter," Pasadena police Lt. John Dewar said.

Dewar said the note mentioned “some kind of possible violence on Friday” and that school district officials contacted police on Tuesday.

The department will deploy extra officers to the campus, but “I don’t think there’s been anything to substantiate [the threat] at this point,” Dewar said.

The police presence is the result of “an abundance of caution,” Wolfson said, adding that the school is expected to stay open the remainder of the week.

“In today’s climate, we take everything seriously,” he added.

The telephone message urged anyone with information about the threat to contact campus officials or report it anonymously by calling (800) 78-CRIME [27489]. The school district also operates a text message emergency alert system. To join, text “PUSD” to 888777.

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joe.piasecki@latimes.com