Mexican authorities are investigating the deadly fire that erupted at a state-run natural gas facility in northern Mexico, killing at least 26 people Tuesday. The fire has been extinguished, but seven people remain missing.

Mexican state oil and gas company Petróleos Mexicanos, or Pemex, initially reported that the fire at the natrual gas pipeline distribution center near the city of Reynosa in Tamaulipas state had been caused by a gas leak that had ignited, though the causes of the leak have yet to be determined.

Pemex Director Juan Jose Suarez said that fire appeared to be “an unusual accident” and that there was “no evidence that it was a deliberate incident or some kind of attack,” according to the BBC.

Similar accidents in the past have been linked to illegal taps on pipelines, though criminal gangs have typically targeted fuel pipelines supplying gasoline or diesel, rather than natural gas.