Mexican police seized more than 20 kilograms of heroin stuffed under the fenders of a truck that two siblings were driving to the United States, federal authorities said.
Police stopped the brother and sister, aged 21 and 24, on a road near the northern city of Monterrey on Monday after a tipoff about trucks traveling overnight with armed escorts in the area, the public security ministry said in a statement.
The siblings said they lived in California, it added.
The seizure of 20.6 kilos of heroin was a record for the northern state of Nuevo Leon, according to local authorities.
Seizures of cocaine and marijuana are common in the major drug corridor between South America and the United States, but opium plantations also exist in western Mexico.
An explosion of drug-related violence left more than 5,300 people dead last year alone, particularly in northern areas, despite a government clampdown involving more than 36,000 troops.