UPDATE: Officials said on Monday afternoon that schools in Nashua will reopen on Tuesday, but with a heavy police presence, the Boston Herald reports.

Parents in New Hampshire’s second-largest school district received a disturbing message on Sunday night: classes would be canceled Monday after officials received a threat against the student body over the weekend.

“We felt that given the specificity of the threat and the fact it was referencing our two high schools, which represent a third of our district, we would close all of our schools to be on the conservative side for safety today,” Superintendent Mark Conrad told The Post Monday morning.

The threat, sent to an administrator over the weekend, was “very specific,” citing the day, location and manner in which an attack would be carried out, Conrad said. He would not describe the nature of the threat, but said local law enforcement is working with the FBI to assess its credibility. The district receives threats from time to time, usually from within the 11,500-pupil student body, but few are as specific as the one received this weekend.

“It’s been eight or nine years since we’ve received a specific threat to a school, so this is not something that we see very often,” Conrad said.

While the threat only referred to the two high schools, officials decided to close all 17 in the district since parents of students in those other schools would worry about the safety of their children and likely keep them home anyway.

Nashua’s decision comes less than a week after officials in Los Angeles, home to the nation’s second-largest school district, canceled school there after receiving an emailed threat. Schools in New York City, the nation’s largest school district, remained open despite receiving the same threat.

Officials in New York were critical of Los Angeles over its decision. Mayor Bill de Blasio (D) said he chose to keep schools open because he did not want to “aid and abet” those seeking to create panic. New York City Police Commissioner William J. Bratton, who was formerly chief of police in Los Angeles, said L.A.’s decision was “a significant overreaction.”

Attacks like the one at Sandy Hook Elementary School—not to mention San Bernardino and the like—have school officials throughout the country concerned about the safety of their students.

In Nashua, the district recently spent more than $2 million to overhaul its security systems, a process that began before the Sandy Hook shooting, in which 27 victims were killed, most of them elementary school children.

The overhaul included locking down all main entrances so visitors have to be buzzed in, installing security cameras around schools, adding door alarms and adding “Columbine locks” throughout the district, which allow teachers to lock classrooms from the inside.

“We’ve worked very hard to improve that safety and security,” Conrad said.

Nashua schools are expected to open again on Tuesday as scheduled, unless new information or a new threat surfaces, he said. Parents and staff will receive another phone call tonight either way.

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