NEWTOWN, Conn. (CBSNewYork/AP) — Visitors were barred from Newtown High School in Newtown, Connecticut for the afternoon Tuesday, after school officials discovered a threat on social media.

Schools Superintendent Joseph Erardi sent an email to parents Tuesday notifying them of the lock-in at the high school.

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The lock-in allowed classes to continue on a normal schedule, but increases security and prevents visitors from entering the building.

The threat follows an evacuation last month at the temporary Sandy Hook Elementary School in Monroe following a threat received there. Building and grounds were checked following that threat, and no evidence of danger was found.

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The original Sandy Hook Elementary School, since demolished, was the site of the December 2012 mass shooting that took the lives of 20 first-grade students and six educators.

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