( CNN ) -- Gunmen attacked a nightclub in northern Mexico on Monday night , killing at least nine people , a police spokesman said . The unidentified gunmen entered a nightclub in the city of Monterrey late Monday , opening fire on the staff and clients of the Men 's Club Matehuala , said Jorge Domene , a Nuevo Leon state security spokesman . Among the dead was a man who tried to escape through the roof of the bar and fell to his death into a neighboring establishment , Domene said . Northern Mexico is among the areas most affected by drug cartel violence as police crack down and rival gangs attack one another for control of lucrative smuggling routes .
Gunmen attacked a nightclub in Monterrey , Mexico , on Monday night . The gunmen were wearing masks and armed with automatic weapons.