New York police arrested a high school sophomore who had a pistol in his backpack with 13 rounds in the magazine, officials said.

Authorities in New York City said they prevented a potential high school shooting after the FBI, acting on a tip, alerted them to a social media post that appeared to threaten to "shoot the school up," officials said Thursday.

The 16-year-old student was arrested at Queens' Benjamin Cardozo High School after he was found with a .9 mm handgun that had 13 rounds in the magazine, New York City Police Commissioner Jessica Tisch told reporters.

Tisch did not say what charges the sophomore may face.

The student, who was not publicly identified, was taken into custody at 12:36 p.m., roughly two hours after he posted the message on Instagram, Tisch said, noting that authorities believe he wrote the post at school.

A screenshot of the post shared by the New York Police Department showed a photo of schoolwork with a short message that included "boutta shoot the school up."

A spokesperson for Instagram declined to comment.

New York City Mayor Eric Adams said a tipster initially alerted authorities to the post. The FBI became aware of it at 11:33 a.m. and provided information associated with the Instagram account -- including the user's phone number and geolocation -- to New York City police, Tisch said.

The student was removed from class without incident and brought to a conference room, where investigators dialed the phone number associated with the account, Tisch said.

After the student's phone rang, authorities requested consent from the teen's mother to search his bag, Tisch said. Inside they found the loaded Taurus .9 mm., she said.

In a statement, the FBI's New York City field office said the swift response "demonstrates the importance of close partnerships and the critical need for information-sharing to ensure our city and students are protected against unnecessary acts of violence."

"This was a failure of a society that allows 16 year olds to get so close to shooting up a school and potentially killing classmates and teachers," Adams said.

A social media post, a tip and an arrest: NYC officials say they stopped a possible school shooting