The field was littered with half-burned shoes and clothes as well as with buckets and drums used by people to collect fuel. Relatives of victims stood huddled together, some crying.
Lopez Obrador pledged to step up his government's drive to stamp out fuel theft, which has cost the country billions of dollars in the last few years. Video footage showed residents scrambling to fill containers from the burst pipe and badly burned victims, raising questions about the management of an issue Lopez Obrador has made a top priority since taking office on December 1.
Veteran leftist Lopez Obrador launched a crackdown on fuel theft on December 27 and ordered pipelines to be closed temporarily to stop illegal taps draining billions of dollars from the heavily-indebted state oil firm Petroleos Mexicanos (Pemex).
"Far from stopping the fight ... against fuel theft, it's going to become stronger, we'll continue until we've eradicated these practices," Lopez Obrador said early on Saturday. Video on social media of people filling buckets from the pipeline during daylight hours in the presence of the armed forces prompted questions about why authorities had not acted.
The government said soldiers reached the scene after Pemex detected the illegal tap, but could not secure the area in time. "At some point there were too many people there and the army and military personnel withdrew to avoid problems," Public Security Minister Alfonso Durazo told broadcaster Televisa. "It was just as they were withdrawing that the explosion occurred.