Mexican army soldiers confiscated 245 kilos (540 pounds) of opium gum, the country’s largest-ever seizure of that substance, the Defense Secretariat said.
The operation, in which two people were arrested, was carried out at a home in the capital of the southern state of Guerrero, Chilpancingo, the scene of a bloody turf war among drug cartels in 2010.
The 245 kilos had a street value of 148.2 million pesos (some $12.1 million) and could have been processed to make 612,500 doses of heroin.
The army, given a leading role in the fight against drug trafficking in December 2006 by newly inaugurated President Felipe Calderon, did not indicate when the seizure was made nor how it learned of the consignment.
The strategy has led to the elimination of several crime bosses and record drug seizures over the past four years, including the confiscation of 23 tons of cocaine in a single operation in November 2007.
Yet the amount of seized drugs represents a small percentage of the estimated total that originates in or is smuggled through Mexico.
Some 400 tons of cocaine from South America are smuggled into Mexico annually. Much of that total is taken across the border to the United States, although in recent years a sizable portion has remained in Mexico to meet local demand.
More than 34,000 people have died in drug-related violence since Calderon took office.