The blast occurred near Tlahuelilpan, a town of 20,000 people about an hour's drive north of Mexico City.
"We're not going to fight fire with fire", the veteran leftist said.
According to the government of Hidalgo state, the pipeline was ruptured by suspected fuel thieves filling up containers. Fuel thieves broke open an oil pipeline in an alfalfa field, and a huge geyser of gasoline burst out, carrying flames through the air.
Several of the deceased lay on their backs, their arms stretched out in agony. A few corpses seemed to embrace each other in death.
But he acknowledged that investigators would be hampered by the fact that "the people closest to the explosion died".
Authorities blamed fuel thieves for this incident as well.
The cause of the explosion, said state oil company Petroleos Mexicanos (Pemex), was a rupture caused by illegal tapping of the pipeline.
The crackdown involved state oil firm Pemex changing its distribution mechanism, triggering fuel shortages, empty petrol stations and long lines of angry motorists.
The president, who took office on December 1, has vowed to keep up the fight and asked Mexicans to be patient. This, besides being unlawful, puts your life and that of the families at risk.
Mexico explosion: at least 20 killed after burst pipeline ignites
On Friday night at about 5 pm, a group of people collecting fuel from a gas line were hurt when an explosion occurred.
"I urge the entire population not to be complicit in fuel theft", saidHidalgo Governor Fayad.
"A lot of innocent people came here, perhaps their auto didn't have enough gasoline for tomorrow, and they said I'm just going to go for a few liters", said farmer Isidoro Velasco, 51, who was waiting for news of his nephew Mario Hidalgo, who he believed likely dead. But in recent days, as the government cracks down on fuel theft rings, the gangs have punctured pipelines and invited locals to help themselves.
Romero said about 10,000 barrels of high octane gasoline were in the section of the pipeline between the Tula refinery and the village when it blew up on Friday.
The government has shut off key pipelines until they can be fully secured and deployed the army to guard Pemex production facilities.
More than 100 people gathered at a local cultural centre on Saturday afternoon, hoping to get information about loved ones who disappeared.
Health officials were taking DNA samples from direct relatives at the local community center in Tlahuelilpan to aid in identification.
"Ay, no, where is my son?" he wailed. There aren't enough trucks, however.
President López Obrador travelled to the scene in the early hours of hours of Saturday.