Extra police have been patrolling schools in a New Hampshire district that closed for a day following a threat to hurt students and teachers.

Nashua (NASH'-wuh) Police Capt. David Bailey says 13 extra officers were in the schools Tuesday; usually there are three school resource officers. Other patrol officers also were asked to do frequent checks when they weren't on a call.

School Superintendent Mark Conrad says the district's two high schools had about 65 to 70 percent attendance, compared to the normal 90-plus percent.

The threat received by an administrator Sunday targeted the high schools in the state's second-largest district. Administrators, acting out of caution, closed all the schools Monday. By that afternoon, police said they had determined it was safe to send kids back to class.