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San Diego police were investigating Monday a report of a threat at Mt. Carmel High School in Rancho Peñasquitos.

“Significant police resources” were sent around 9 a.m. to secure the campus while officers investigated whether the threat was credible.

According to an announcement being played over the school’s loudspeaker, a potential bomb threat was made, which prompted the huge police presence.

Sunset Hills Elementary and Black Mountain Middle School were also placed into a secure campus as a precaution. Secure campus means class instruction continues as normal while campus access is limited.

Video from a parent at Mt. Carmel showed several law enforcement vehicles with rifles walking toward campus. A U.S. Marshal vehicle was on site as well as the San Diego Fire-Rescue Department.

At least 100 parents were outside the school waiting for updates from school officials or police. Students could be seen exiting classrooms in small groups.

This is a developing story. Details may change as information is released.