A pencil drawing on a classroom desk in a Queens high school last week was the source of a social media post displaying a threatening message that disrupted Long Island school districts on Monday, the New York Police Department said Tuesday.

A student at Hillcrest High School, in the Jamaica Hills section, saw the image on Feb. 27 that Sgt. Jessica McRorie described as having wording about “threatening to shoot up the school.”

The student who saw the threat reported it to a teacher, she said.

Subsequently, someone took a picture of the threat and shared it via Snapchat, McRorie said.

Districts across Nassau and Suffolk counties enacted heightened security measures Monday as parents and school officials reported a threatening Snapchat post that had circulated widely.

McRorie said that Nassau County police, after learning of the Snapchat post, “reached out to us. We had the initial investigation.”

No arrests have been made. McRorie said the department is continuing to investigate. She noted that the threat referred only to the Queens school.

Nassau police did not provide further information on Tuesday.

Hampton Bays Superintendent Lars Clemensen, who serves as president of the Suffolk County School Superintendents Association, said there had been a lot of chatter about the Snapchat image on Facebook groups over the weekend.

Clemensen, who sent a letter to Suffolk residents Monday on behalf of the association, said in an interview Tuesday that people should direct reports of threats to the authorities and school officials.

“If you have a concern about something, pick up your phone, don’t pick up the keyboard,” Clemensen said. He noted that “many schools were finding out about this because the Facebook community pages were on fire about this, as opposed to a formal call to the school districts.”

He added that the episode caused alarm among Long Island’s top school administrators. “That’s where superintendents woke up this morning thinking this new reality. This was a major disruption across Long Island over the last 72 hours, and the message to parents, communities and students: Report it immediately.”

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