The children of the employees killed in the explosion last week at the Mexico City headquarters of state-owned oil giant Petroleos Mexicanos, or Pemex, should be allowed to inherit their parent's jobs, oil workers union leader Carlos Romero Deschamps said.

Meetings will be held with the dead workers' relatives and with employees injured in the blast so they can receive all the assistance needed, Romero Deschamps said.

"In the case of the dead workers, where the father or mother died, we are going to propose that the son or daughter be allowed to work permanently so that they can take care of the family, which was left without support," the union leader told Mexican media.

The goal is to preserve the jobs of workers who had permanent contracts and convert the temporary positions to permanent ones, Romero Deschamps said.

"From the union and human standpoint, it is the least we can do in light of a tragedy of this magnitude," the union leader said.

The explosion at Pemex headquarters last Thursday killed 37 people and injured more than 100 others.

The blast was caused by an accumulation of gas, Attorney General Jesus Murillo said earlier this week.

The explosion was not caused by a bomb because laboratory tests found no traces of explosives in the rubble, the AG said.

The explosion was likely caused by an accumulation of methane gas ignited by a spark, Murillo said.

Workers were doing maintenance on the structure's support columns when the blast happened.

The main tower of the office complex, a 56-story structure, was not damaged in the blast. EFE