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.

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

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.

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