MEXICO city - A police raid on a crammed Mexico City nightclub on Friday turned into a deadly stampede that killed 12 people, including nine youths and three police, officials said. Police entered the New Divine nightclub, where around 1,000 people had gathered to fete the end of the school year, to break up the illegal sale of alcohol to minors and a stampede ensued, said Joel Ortega, a local security official. "Unfortunately, the person in charge of the nightclub took the microphone and announced a police operation was underway," Ortega said, adding that his words "sparked a panic." People rushed to get out, causing a stampede. Cases of beer were blocking the emergency exit, officials said. Seven youths - three of them young women - and three police died at the scene. An 18-year-old and a 15-year-old succumbed to injuries in the hospital, where around 20 others were rushed for treatment. "The deaths were attributed to asphyxiation by suffocation," said public prosecutor Rodolfo Felix. The raid took place around 2330 GMT, about an hour and a half after the gathering kicked off. A ticket to enter the party cost three dollars, and the two-story, 20 square meter space quickly filled beyond capacity. The capital's main nightly newscast broadcast a brief video that was taken by police at the moment when officers entered the premises. In the video, a cloud of smoke appears on the dark premises, youths can be heard shouting and a disc jockey says in a calm voice over a loudspeaker: "We are going to evacuate the place, there is a police raid." People were continuing to line up outside the club in the hopes of entering as the raid was announced. Police arrested three nightclub employees and 39 other people on charges of disturbing the peace. Authorities said there was no exchange of gunfire and denied using teargas on the crowd. Abandoned shoes lay scattered outside the entrance to the discotheque, and a group of youths briefly returned to the scene to throw stones at a hundred or so police officers who remained outside. Asked if police took adequate precautions to avoid the tragedy, Ortega answered: "Many plans are made ahead of time, but a lot depends on the attitude of the people inside and how the group behaves."