A city prosecutor says three people were shot dead in a tough Mexico City neighborhood that is home to the area's biggest black market.
Prosecutor Alberto Ramos says one person was also injured. He did not give more details about the shooting late Thursday night.
Mexican media said the shooting happened inside a gym in Tepito, one of Mexico City's most dangerous neighborhoods.
Tepito is home to 12 people who were kidnapped nearly two weeks ago from an after-hours bar in the city center. Three people have been detained in the kidnapping, but there is still no sign of the 12 who were taken in broad daylight May 26 by heavily armed and masked men.
It was not immediately clear if the shooting had anything to do with the kidnapping.