Culiacán: Clashes killed 19 gunmen and injured five police officers in the northern Mexican state of Sinaloa, the heart of operations of some of the country’s biggest drug traffickers, authorities said Saturday.

The incident occurred late Friday when a group of gunmen clashed with Mazatlan city police who were on a routine tour led by local police chief Joel Ernesto Soto.

The confrontation began around 8:00pm (0100 GMT) in the town of Villa Union when police repelled the gunmen’s assault, Sinaloa deputy secretary of security Cristobal Castaneda said.

The 19 men, who were riding in four vehicles, pursued their confrontation by a highway, where they were killed by municipal police.

‘They faced quite a number of aggressors, but thanks to their training and professionalism, they managed to get ahead. The wounded policemen are well,’ Castaneda told reporters.

At the scene of the clash, four vehicles, 15 rifles and seven handguns were found.

Officials said the fighting was some of the worst in the southern part of the state in recent months, since a battle errupted over the restructuring of the powerful Sinaloa cartel following last year’s capture of its leader Joaquin ‘Chapo’ Guzman.

The internal war over the group’s leadership has led to escalating violence in Sinaloa this year, with more than 760 murders in early June, a figure not seen since 2011, according to the state security secretary.

Violence has also increased in other states. The latest available official data indicate that May was the deadliest for Mexico since official records began in 1997, with a total of 2,186 wilful homicides.