PICO RIVERA (CBSLA.com) — Authorities Wednesday are investigating a threat that was made towards a middle school in Pico Rivera.

Around 6 a.m., an unidentified man reportedly phoned in a threat to Rivera Middle School, located in the 7200 block of Citronell Avenue, according to the Pico Rivera Sheriff’s Station.

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School officials explained the threat was made before school started.

Deputies have set up a perimeter around the school, and are investigating the credibility of the threat.

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At this time, it remains unclear what the threat entailed.

According to the El Rancho Unified School District, the middle school and Rivera Elementary School will remain closed today. Classes will be held on Thursday.

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No injuries were reported.