A massive fireball that engulfed people scooping up fuel spilling from a pipeline ruptured by thieves in central Mexico killed 66 people and badly burned 76 others in what was a chronicle of a tragedy foretold.
Video taken before the explosion shows how some 700 people gathered at the pipeline as it sent a jet of gasoline into the air, while army soldiers stood by, apparently doing little to intervene.
Alcocer said in an early Sunday news conference that some patients are in serious condition, with burns on more than 80 percent of their bodies and organs compromised following the accident.
Video footage showed dozens of residents in an nearly festive atmosphere as whole families gathered in a field as a geyser of fuel spouted dozens of feet into the air from the tap.
"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, who has said he will step up the security presence in sensitive areas, said.
Acting Attorney General Alejandro Gertz claimed the explosion was "intentional" because "someone caused that leak".
"A lot of people arrived with their jerry cans, because of the gasoline shortages we've had", said 55-year-old Martin Trejo, who was looking for his son, who had gone to collect the fuel.
State oil company Pemex said an investigation is under way.
Fuel thieves punctured the Tula-Tuxpan pipeline a few miles from one of Mexico's main refineries on Friday. The most recent efforts started late in December, which included closing the pipelines.
"I am deeply saddened by the suffering in Tlahuelilpan", Lopez Obrador wrote on Twitter.
One witness described how an nearly festive atmosphere among hundreds of local residents filling containers with spilled fuel turned to horror as the blast scattered the crowd in all directions, incinerating clothing and inflicting severe burns.
Lopez Obrador, who has launched a crackdown on fuel theft, called on "the entire government" to assist the people at the site of the explosion.
It was not clear if those actions included shutting off the flow of fuel in the pipeline. This caused in some cases lengthy delays in fuel deliveries, with the shortages even reaching the capital of the country, Mexico City.
Health officials were taking DNA samples from direct relatives at the local community center in Tlahuelilpan to aid in identification.
Pemex attributed the blaze to "the manipulation of an illegal tap". In a statement, PEMEX announced that the explosion was caused by the illegal manipulation of the pipeline, as minutes before the accident videos were shot where people could be seen filling drums and vehicle fuel tanks.
Romero said Pemex closed a valve at the pipeline on Friday after noting a drop in pressure from the leak.