Most natural gas distribution networks are vulnerable to overpressurization which might cause city-wide fires and hundreds of casualties, a few terrorists can organize that by physically capturing relevant infrastructure. But for that they need technical competences which they lack, as no contemporary violent non-state actors really reach the sophistication of Aum Shinrikyo.
Your plan, however, requires not only engineering skills but time and money and production facilities. It’s not impossible that another AS-like apocalyptic sect will emerge in the future but it seems unlikely. Hezbollah might have the means to develop capability in the near future (as Yair Halberstadt has rightfully noted below) and it may be a natural outgrowth of their current drone program but they won’t be able to keep the program secret from Israeli intelligence
Most natural gas distribution networks are vulnerable to overpressurization which might cause city-wide fires and hundreds of casualties, a few terrorists can organize that by physically capturing relevant infrastructure. But for that they need technical competences which they lack, as no contemporary violent non-state actors really reach the sophistication of Aum Shinrikyo.
Your plan, however, requires not only engineering skills but time and money and production facilities. It’s not impossible that another AS-like apocalyptic sect will emerge in the future but it seems unlikely. Hezbollah might have the means to develop capability in the near future (as Yair Halberstadt has rightfully noted below) and it may be a natural outgrowth of their current drone program but they won’t be able to keep the program secret from Israeli intelligence