CLIFTON, N.J. -- Five elementary school students were detained after allegedly plotting to "cause damage" or "detonate a device" at Clifton High School in New Jersey, authorities said, according to CBS New York.

According to authorities, teachers and administrators found suspicious letters from the students claiming they were going to "attack" the school. The school then notified the Clifton Police Department.

The students were all between the ages of 10 and 11 years old, police say. Authorities say they attend a kindergarten-through-5th grade school.

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CBS New York reports that police say they found a "suspicious device" when investigating the threat, but the device was later proven to be non-explosive.

According to police, this does not appear to be a prank.

The five detained children have since been released to their families, according to police. Their names will not be released because of their ages.

According to police, this was an isolated incident and there are no current safety issues at the school.

CBS New York has reached out to the Clifton Public Schools Superintendent.

Clifton Police Department is working with the Passaic Prosecutor's Office to determine if there will be any charges.