Thirty people were killed and seven more suffered gunshot wounds over just two days of drug trafficking-fuelled violence in the Mexican state of Chihuahua, a spokesman said Saturday.
The 30 were killed on Thursday and Friday in the northern state, which borders the US, while another died Saturday of serious injuries.
Carlos Huerta, the spokesman for the local prosecutor's office, said the violence was due to attacks by the rival Juarez and Sinaloa cartels.
Of the 31 deaths, 22 occurred in Ciudad Juarez, seven in state capital Chihuahua and two in Bocoyna, authorities said.
Among the dead were four women and three adolescents aged 14, 15 and 17.
More than 250 members of the federal police were to be deployed in the area on Saturday.
Shortly before the series of killings began, state Governor Javier Corral said that 2018 would be the "year of public security for Chihuahua."