A massive security operation is underway in Mexico, as the government steps up the war against drugs cartels.The surge, one of the biggest in years, comes after a dozen federal police were found murdered in drugs-related violence. Heavily-armed soldiers have set up roadblocks in the flashpoint western state of Michoacan. That is where the remains of 11 men and one woman working for federal authorities were dumped on a highway, bearing signs of torture. Ten local police have been detained on suspicion of collaborating in the murders. A warning message was found with the bodies. The latest episode in Mexico’s long history of drugs-related bloodshed was revenge for the capture of a high-ranking member of the local cartel. More than 7,700 people have been killed in Mexico in violence linked to organised crime since 2008, according to government figures.