Mayor Bill de Blasio reiterated his faith in Police Commissioner Bill Bratton yesterday, in light of new video that apparently shows cops beating a teen during an arrest.

In the video, first reported by DNAinfo.com, officers appear to be punching a teenage boy as they arrest him. They had allegedly chased 16-year-old Kaheem Tribble down just after 1 a.m. on Aug. 29, said the teen's attorney, Amy Rameau.

"He's just a kid and he's absolutely petrified," Rameau said. "He's afraid that these cops are going to try to come back and try to hit him. These officers did a number on him."

Rameau said they broke Tribble's teeth and caused swelling when one hit him with the butt of his gun. The charges against Tribble of possession of marijuana and resisting arrest, she said, were dismissed.

The record of Tribble's arrest was sealed, police said. His arraignment information was not available, said a spokeswoman for the Brooklyn District Attorney's office.

"What's depicted on this video is troubling and warrants a thorough investigation," Brooklyn DA Ken Thompson said in a statement yesterday. Officials did not release the names of the officers.

In the video, one of the officers can be seen running up to Tribble and allegedly punching him. Tribble then raises his hands up as a second officer allegedly walks up with his gun held high before apparently hitting the Tribble with the gun.

Tribble then appears to lay on the ground for a few seconds until the first officer allegedly punches him again. A third officer then walks up and the first officer handcuffs Tribble.

"I think the fact is, that we're getting a kind of information we didn't used to have before the age of the cell phone camera, and we're seeing some things that -- maybe they existed in large measure before, we can't tell for sure because we didn't have the documentation," de Blasio said at an unrelated news conference Tuesday. "We do know now what we're seeing, and it's important that every time we get evidence of something that might have been done wrong that there's a full investigation, and where appropriate, that there are consequences."

One of the officers involved in the incident has been suspended without pay and one has been placed on modified duty, police said. "The matter is under internal review," said NYPD Deputy Chief of Public Information Kim Royster.

"Clearly, Commissioner Bratton has seen the video and reacted very aggressively in the sense of saying that there have to be consequences when anything is done the wrong way," de Blasio said. "I think the Commissioner has set a very clear standard and I commend him."