Israel targeted Hezbollah leader Hassan Nasrallah with an airstrike on the group’s headquarters in Beirut, the heaviest attack on the Lebanese capital in almost two decades and a major escalation of a conflict that threatens to engulf the Middle East.

Israel began to signal that its campaign against Hezbollah had expanded in July when it targeted one of the militant group’s senior commanders, Fuad Shukr, in Beirut’s southern suburbs. Previously, the low-grade conflict between Hezbollah and Israel was largely confined to the border region in southern Lebanon.