The civilian self-defense forces had their eye on Apatzingan for months, saying it was the "crown jewel" of the Knights Templar gang and a vital trade hub for the region's lime and avocado farmers.

Vigilante leader Estanislao Beltran said that hundreds of his colleagues manned checkpoints outside the Michoacan state city of 120,000 to "check who goes in and out."

Heavily armed men were seen building walls of sandbags outside Apatzingan, the main city in Michoacan's Tierra Caliente (Hot Land), a lush agricultural region....