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QUEENS, N.Y. — Windows were smashed on two more No. 7 trains Friday night, police said, as the MTA warns that the ongoing vandalism could impact service.

Patrick Warren, the MTA’s chief safety and security officer and acting COO of MTA NYC Transit, said 21 windows were busted on two trains.

Damage on one train was discovered just before 10 p.m. in the Vernon Boulevard-Jackson Avenue station. The second train was found vandalized just after 10 p.m. at the 103rd Street station, according to Warren.

Officials believe the vandalism is happening from inside the train using a blunt object while the train is in motion, Warren said.

The motive behind the vandalism remains unclear, but it’s costing the MTA hundreds of thousands of dollars.

The smashed windows from Friday night alone cost the cash-strapped transit authority an estimated $10,000 in damages, Warren said. In all, the MTA has seen over 400 smashed windows since the spring, which cost a whopping $300,000 in repairs.

Warren called the vandalism “intolerable.”

“This is absolutely infuriating for the people of New York and, of course the MTA, to have to continue to work through this challenge of vandalism on our system,” Warren said. “It is costing New York City customers, the taxpayers money.”

The smashed windows also impact subway service. Every time a broken window is found, that train is immediately taken out of service and cannot return until the damage is repaired.

Currently, it takes several hours to replace a window but the MTA’s stockpile has been depleted because of the ongoing vandalism.

“For that period of time … our customers are inconvenienced with longer wait times and potentially more crowding on the platforms,” Warren said. “We have yet to have to pull trains out of service for extended periods of time, but that’s certainly a possibility going forward.”

Police have released a photo of at least one suspect wanted in connection with some of the vandalism.

The man is suspected to be involved with at least 64 incidents where glass was broken on train cars along the No. 2, 3 and 7 lines in Manhattan, Queens and the Bronx between May 8 and Aug. 3, according to police.

An NYPD spokesperson said there is no suspect description related to the two incidents reported Friday night.

The MTA continues to work with the NYPD on increasing surveillance, but Warren also called on police to implement a “broken-windows strategy.”

“And we certainly would like to continue to work with the NYPD on that strategy if they choose to take that,” he said.