TRENTON, Sept. 21 (AP) — Two North Jersey high school students have been accused of making a copycat bomb threat after a similar threat closed schools in 12 districts.

On Thursday, a note threatening a bomb attack was slipped under a gym teacher’s office door at Hackensack High School, officials said. The day before, officials in 12 North Jersey school districts canceled classes in response to a bomb threat received in the mail in Emerson.

Police officers said they traced the Hackensack note to two 17-year-old juniors from Rochelle Park. Hackensack Police Chief Charles Zisa would not say how they were identified or disclose their names, since they are juveniles.

The note warned that bombs would be used to blow up the school, Chief Zisa said, and the note was signed “Alcada,” presumably referring to Al Qaeda.

The two students suspected of writing the note were called to the principal’s office and arrested on Thursday afternoon, Chief Zisa said.

They have been charged with terrorist threats and false public alarm. Chief Zisa said the authorities were considering whether to use a more serious charge, threat of terrorism, and also whether to charge them as adults, since they are a few months from turning 18.

By Friday, the two had been suspended from school. Electronic monitoring devices were attached to them to make sure they did not leave their homes except when county government workers were taking them to and from the juvenile detention center for classes, Chief Zisa said.

The police believe the note was a copycat, imitating a letter sent earlier in the week to the borough hall in Emerson that caused the closing of schools in 12 towns. The schools reopened on Friday.

There was also some fear on Thursday at two Wood-Ridge schools. A middle school and a high school were evacuated after a student reported overhearing talk of a bomb. Police checks found nothing.