HATBORO, Pa. (CBS) – Two Philadelphia area schools were placed in lockdown on Monday.

Around 10 a.m., the Hatboro-Horsham School District sent out an email message that stated that Hatboro-Horsham High School and Simmons Elementary School were in lockdown.

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Parents and guardians were told not to call the school, and there was no information on why the schools were locked down.

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The District later said that it had received a threatening phone call at Simmons Elementary. The school and grounds were searched by police for about 25 minutes and nothing was found.

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Classes have since resumed and additional security will be in place throughout the school day.