ELYRIA -- Police say Elyria High School was placed under an exterior lockdown Friday morning after a trio of threats on the school were made via telephone.

According to police, the calls were made just before 8:47 a.m. The caller, who police say may be a man in his early 20s, indicated that a subject planned on causing harm at the school. Police say three calls were made, seemingly by the same person, in quick succession.

The school was placed on an exterior lockdown for an hour.

Police say they are working to determine who made the threats.