Mexico's government has sent hundreds of police reinforcements to the Sinaloa region to deal with a wave of police killings in drug wars.
Several thousand troops and police are already working in the centre of Mexico's drug trade.
But they've been unable to stop police killings and feuding drug gangs. In a strong blow to Mexico's three-year drug war, seven police officers were murdered on Tuesday in Sinaloa, home to Mexico's most-wanted drug kingpin, Joaquin "Chapo" (Shorty) Guzman.