Officials say at least 29 people were slain on the first day of 2016.
Prosecutors say the worst attack came when armed men in military-type uniforms raided an evening party of suspected gang members and killed six in the town of El Zapote, 130 kilometers southeast of the capital. It followed a pre-dawn slaying of five people in Los Cerritos, 160 kilometers east of the capital.
Police also say they killed five presumed gang members in another clash.