SAN MATEO -- School officials and police here Wednesday became the latest in the Bay Area to respond to apparent hoax threats made either online, by telephone or graffiti against their campuses.

Early in the day, a student alerted school officials to undisclosed threats on a Facebook "confession" page to be carried out Thursday against Aragon High School. Police were notified.

It doesn't appear the threats are "credible" said Associate Superintendent Kirk Black of the San Mateo Union High School District. Nonetheless, authorities beefed up police presence at the school Wednesday and into Thursday.

"I assume it will be the safest campus in the country with all the cops that will be there," Black said.

The threats in San Mateo came on the heels of a string of similar incidents in cities such as Fremont, Tracy and Pleasanton. On Monday, Thornton Junior High School in Fremont received its third threatening phone call in less than a week.

A 14-year-old student at the school was arrested March 14 on suspicion of making threatening calls to the school. Because he's a juvenile, his name hasn't been released. Threats at other campuses have included graffiti scrawled on school property.

San Mateo officials didn't say whether they think a trend is developing. The threats don't appear to be related, and it's unclear whether the threats have been inspired by a web posting or online video.

"I haven't heard anything like that," said San Mateo police Sgt. Dave Norris. "If we find something like that, we will pass it along."

Police are working with the school district and Facebook to investigate, and they say offenders will be held accountable. Anyone with information can call San Mateo police at 650-522-7700.

Contact Joshua Melvin at 650-348-4335. Follow him at Twitter.com/melvinreport.