NEW YORK (CBSNewYork) — Two young teenage boys faced charges late Monday after one of them allegedly took out a gun and threatened a girl in an Upper East Side school.

Around 1:45 p.m., 19th Precinct officers were called to P.S. M169 Robert F. Kennedy, at 110 E. 88th St., by school staff, according to the NYPD.

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The officers went to the administration office and arrested three boys, ages 13, 14, and 15, police said.

The 13-year-old boy had come to school with a fully-loaded .22-caliber revolver stuffed in his hoodie, according to Teamsters Local 237, which represents school safety officers. Police sources told CBS2 the boy took out the gun and threatened a 12-year-old girl at the school.

Police said the 15-year-old boy had taken the handgun at the time of the arrests, and the 14-year-old boy had an extra box of ammunition, CBS2’s Valerie Castro reported.

The 13-year-old, from the Bronx, was later charged with criminal possession of a weapon and menacing, while the 15-year-old, from Manhattan, was charged with two counts of criminal possession of a weapon, police said.

The 14-year-old had not been charged late Monday.

“This incident is deeply alarming and we are working closely with the NYPD as they investigate this extremely disturbing report. Nothing is more important than the safety of all students and staff and there is zero tolerance for weapons of any kind,” the New York City Department of Education said in a statement. “Students and staff are safe and no injuries were sustained. Parents will be notified and we are providing ongoing supports to the school community.”

Multiple students have allegedly been caught with guns in school in high-profile incidents around New York City in recent weeks.

On March 22, a 14-year-old boy allegedly brought a 9mm semiautomatic weapon and two magazines containing nine rounds into M.S. 61 Dr. Gladstone H. Atwell, at 400 Empire Blvd. in Crown Heights, Brooklyn, police said.

Sources told 1010 WINS the student told an administrator that he was armed because he had been involved in some sort of confrontation earlier with unspecified people – but not students – outside of school grounds.

The student allegedly got the gun from a friend, police said.

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The student was charged as a juvenile with criminal possession of a weapon and criminal possession of a weapon on school grounds.

The week before that, students at two schools in Jamaica, Queens were allegedly caught with guns.

On March 17 at York Early College Academy, or YECA a 15-year-old high school student was caught with a .38-caliber gun on campus in Queens.

Police said he was also charged as a juvenile.

Sources said the teen got in a quarrel with a group of students inside the school then opened up his backpack and flashed the weapon.

One of the classmates who saw the gun alerted a school security guard. Students were kept in their classrooms until police arrived.

On March 15, police said an 11-year-old boy brought a loaded 9mm semiautomatic pistol to P.S. 40. His grandfather faces charges, including criminal possession of a weapon.

In another incident involving a weapon on March 29, a 14-year-old boy brought a knife to the Urban Assembly School for Careers in the Mott Haven section of the Bronx, police said.

Teamsters Local 237 President Gregory Floyd said more metal detectors need to be installed at schools.

“These are non-scanning schools that these weapons are being found in,” Floyd said. “This is an indication that scanning needs to be expanded instead of eliminated.”

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In the latest incident on the Upper East Side, it remained unclear late Monday where the student got the gun.