SAN DIEGO (AP) — Authorities say a 15-year-old boy was arrested in a city north of San Diego after posting on social media a threating message directed at his high school.

The San Diego Union-Tribune reports that authorities with the San Diego County Sheriff's Department say the Fallbrook High School student posted a picture of himself holding a gun at a shooting range, warning students to not attend school on Monday.

School officials were alerted to the post on Snapchat and contacted the sheriff's department on Sunday. The teenager was arrested that day and booked into a juvenile detention center.

Authorities say the teenager told investigators that the picture was a joke.

Classes at the high school continued as scheduled on Monday.

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Information from: The San Diego Union-Tribune, http://www.utsandiego.com