NYPD Internal Affairs is investigating four Bronx cops after they were caught on video viciously pummeling and kicking a drug suspect bloody.

The officers, all assigned to the 42nd Precinct in Tremont, were stripped of their guns and shields and placed on modified duty after the footage surfaced on YouTube and other Web sites over the weekend, authorities said.

“We have put four officers on modified duty during the course of our investigation,” NYPD spokesman Paul Browne told The Post last night.

“Their guns and shields were removed while we investigate allegations of police brutality.”

The footage shows five cops first trying to put suspect Jatiek Reed, 19, against a wall on East 168th Street in broad daylight Jan. 20.

The video shows Reed appearing to resist for a moment, throwing a couple of kicks and swats.

Several of the cops then start whacking their nightsticks against the suspect, whose back is against the wall, the video shows. The teen lands face-down on the sidewalk.

“Yo, chill,” one person can be heard shouting on the video.

“No, no, no! Don’t do that,” another one yells.

Three of the cops are then clearly shown repeatedly pounding Reed — kicking, punching and beating him their batons. Another officer, slightly obscured by the others, appears to hold him down.

A fifth cop keeps his distance, walks away, and paces back and forth while talking on his radio.

A cop on the scene then storms toward the person shooting the video and appears to be threatening to nail him with pepper spray while shouting, “Move back, move back!”

The video cuts out soon after.

Reed’s mother, Schuan, told The Post last night that she and her younger son, Jashawn, 17, went to the station house after the incident and were both struck by more than one cop angry that door was slammed on their way out. She insisted neither she nor her son slammed it, claiming it was an automatic door.

Speaking of Jatiek, she said, “He has staples in his head, staples in his arm. His whole back is black and blue like they were beating on a slave. I refuse to let them railroad my son and accuse him of something he didn’t do. If they saw his stash of drugs, then where are the drugs?’’

She added, “If you beat on a dog like that, you go to jail. They should go to jail, too.’’

A law-enforcement source said that before the video began, police saw the teen trying to toss the drugs.

“They go to arrest him, leading him toward the van,” the source said.

“As he realizes he’s being arrested, he tries to get away. They use force that raises questions of excessive force that was captured on video after he was handcuffed.”

The NYPD confirmed the cops will not be given law-enforcement assignments pending the outcome of the investigation.

Bronx DA Robert Johnson is also looking into the matter, officials said.

Jatiek Reed was being held on Rikers Island last night on a slew of assault charges.