An off-duty Secret Service agent fatally shot a dog that apparently charged at him in Brooklyn on Monday night, police said.

The agent fired one shot at the dog, striking the animal, on Caton Place near East 8th Street in Windsor Terrace about 9:45 p.m., cops said.

In a statement, the Secret Service said an employee of the agency opened fire on a “unleashed and aggressive canine.”

Police said the agent saw the dog coming at him as he turned a corner.

Walker Blankinship, who works at the Kensington Stables across the street from the shooting, said he heard the gunshot — followed by arguing between the dog owners and the Secret Service agent.

“There’s a lot of dogs in this neighborhood, I’m used to hearing little snarlings and snappings — usually it’s dog on dog,” he said.

“But I didn’t hear anything until — bang!” he added. “Then I heard people arguing and cursing, ‘Why’d you let the gun go off?’”

Adelaide Gaughran-Bedell, who was near the scene after the shooting, said the dog was “splayed out on the ground” after the shooting.

“And then I think the owner — man and a woman, it was a couple — they wanted to touch her and the police wouldn’t let her. I remember him going to the dog and the sheet,” Gaughran-Bedell said.

The identity of the agent was not released on Monday night.