TLAHUELILPAN, Mexico — Mexico’s president vowed on Saturday to redouble his fight against an epidemic of fuel theft after thieves punctured a pipeline north of Mexico City, causing an explosion that killed at least 79 people and injured 81 others.

The blast underscored the deadly perils of the fuel-theft racket, which has cost the government billions of dollars a year and has been the target of a weekslong crackdown by the administration of Mexico’s new president, Andrés Manuel López Obrador.

The government’s strategy has included diverting fuel from the pipelines most heavily targeted by criminal gangs, and transporting it by truck. But the logistical changes have slowed deliveries across the country, causing shortages and long lines at service stations.