By Stephen Gibbs
BBC News, Mexico City
The army is being called in to tackle drug-related violence in Tijuana
The police chief in the Mexican border city of Tijuana has been removed from his post following a weekend in which 37 people were killed.
State authorities say Jesus Capella, who had received numerous threats, will be replaced by an army officer.
Mexico's border with the US is facing spiralling drug violence, and several police chiefs have either been murdered or arrested on corruption charges.
Three months of violence in Tijuana have claimed more than 300 lives.
Even by the current violent standards of the city, last weekend was particularly gruesome.
Of the 37 people killed, nine men - including three police officers - were found decapitated.
Four children also died, apparently caught in the crossfire.
The city, once known for its tourist attractions, appears to be descending into a battleground between rival gangs.
At stake is control of the immensely lucrative trade of exporting drugs to the United States.
The violence has intensified since Mexican President Felipe Calderon vowed last year to destroy the cartels, which he says threaten the stability of the entire country.
Whatever the specific reasons for Jesus Capella's dismissal, it does reflect the huge challenge the government faces.
With their riches and ruthlessness, the drug runners have successfully bought off or intimidated thousands of Mexican police officers.
So Mr Capella is being replaced by an army officer.
The army is increasingly taking over the task of law enforcement in parts of Mexico, with all the risks that may entail.