Dozens of masked men are heard in video saying they are 'people of Mencho,' a nickname used by Jalisco New Generation Cartel boss Nemesio Oseguera

Almost all of the uniformed men wearing bulletproof vests wield assault rifles, and some appear to have belt-fed machine guns or .50 caliber sniper rifles 

Authorities said they are investigating the video to determine its authenticity 

The cartel based in the central state of Jalisco has spread across Mexico and increasingly has posed direct challenges to the government 

Last month, Mexico City's police chief, Omar García Harfuch, blamed the cartel for an elaborately planned attempt on his life last month