MANHATTAN BEACH (CBSLA.com) — A South Bay high school was closed Tuesday after receiving two security threats against the campus via social media, authorities said.

Officials at Mira Costa High School placed the campus on lockdown Monday morning after an initial threat was found on the anonymous Yik Yak app, the Manhattan Beach Police Department said.

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It read, “If you go to Costa, you should watch out very close at school today.”

The app allows users to post messages anonymously which can be read by anyone within a 1.5-mile radius.

Later that afternoon, “another anonymous social media message went out with another vague and non-specific message: ‘nice try Costa, today was just a drill’,” said Principal Ben Dale in an email to parents.

Administrators originally planned to open the campus Tuesday, but after further contact with police, decided to cancel classes and activities for the day.

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“This includes all activities scheduled from Scholar Breakfast at 7:00 through all athletic and co-curricular activities after school,” Dale said.

Mira Costa officials were expected to contact parents no later than 5 p.m. regarding classes Wednesday.

Heightened security measures were also being taken at other Manhattan Beach schools.

The MBPD is investigating the threats as a criminal matter.There have been at least four other incidents around the country in recent months where security threats were made on the Yik Yap app.

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The Atlanta-based company is working with local police to help identify the suspect.