(CNN) Five students from a middle school in the Mississippi town of Ocean Springs have been arrested on suspicion of making threats to shoot up the school, authorities said.

The students are 13-year-old boys, said Marcia Hill, a spokeswoman for the Jackson County Sheriff's Department.

"These threats are no joke, and Sheriff (Mike) Ezell emphasizes investigators take them seriously," the department said in a news release.

The first student was arrested Saturday at a dance at St. Martin Middle School, she said. Other students heard him threatening to shoot up the school for sixth through eighth grades. Four others who allegedly made mass shooting threats, either verbally or on social media, have been arrested, Hill said.

It's unknown if the students are now being held in jail.

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