Two police officers have been shot dead in a northern Mexican border city which is the focus of a major crackdown on drug trafficking.
It raises to five the number of officers murdered this week in Nuevo Laredo, an important transit point for drugs entering the US.
The Mexican army and federal agents have been sent in to restore order and investigate police corruption.
The operation has resulted in 1,000 arrests but few cocaine seizures.
Ricardo Uvalle Escobedo and Jose de Jesus Morin Salinas were killed by gunmen in separate incidents on their way to work on Wednesday.
On Tuesday night, two other officers, Daniel Juarez and Carlos Manuel Alvarez, were killed when their car was sprayed by automatic gun fire.