Six police killed in Mexico gun attack

Six police officers have been killed by gunmen in the north-central Mexico state of Guanajuato, authorities say.

State Interior Secretary Gustavo Rodriguez Junquera said the dead officers were traffic police and he promised that "this crime will not go unpunished".

Rodriguez Junquera did not say how the attack occurred, but local media reports said the officers were killed by shots fired from a passing vehicle.

Guanajuato was long a relatively peaceful state, but in recent years it has been plagued by crime gangs that rob freight trains and drill into state-owned oil pipelines to siphon off fuel.