Lebanon-based Hezbollah, a radical Shia Islamist political and militant party that has a small share of seats in the country’s parliament, has been designated a terrorist organization by the U.K., the U.S., and other Western nations.

Since Hezbollah-ally Hamas attacked Israel on October 7, 2023, fighting that began decades ago between the Lebanese organization and Tel Aviv escalated.

Nasrallah’s death marks a devastating blow to Hezbollah, which he led for 32 years, as it reels from an escalating campaign of Israeli attacks. It is also a huge blow to Iran, given the major role the Lebanese leader played in the Tehran-backed regional “Axis of Resistance.”

Hezbollah said in a statement that it would continue its battle against Israel “in support of Gaza and Palestine, and in defense of Lebanon and its steadfast and honorable people.” It did not say how Nasrallah was killed.

Iran’s Supreme Leader Ayatollah Ali Khamenei called on Muslims on Saturday “to stand by the people of Lebanon and the proud Hezbollah with whatever means they have and assist them in confronting the … wicked regime (of Israel).”

According to the Iranian state media, Khamenei, in a statement after the Israeli army said it had killed Nasrallah, said: “The fate of this region will be determined by the forces of resistance, with Hezbollah at the forefront.”

The Israeli military said in a statement that Nasrallah was eliminated in a “targeted strike” on the group’s underground headquarters under a residential building in Dahiyeh, a Hezbollah-controlled southern suburb of Beirut.

It said he was killed along with another top Hezbollah leader, Ali Karaki, and other commanders.

“The strike was conducted while Hezbollah’s senior chain of command was operating from the headquarters and advancing terrorist activities against the citizens of the State of Israel,” it said.

Friday’s airstrike on Dahiyeh shook Beirut. A security source in Lebanon said the attack — a quick succession of massively powerful blasts — had left a crater at least 20 meters (65.6 feet) deep.

The attack, followed on Saturday by further airstrikes on Dahiyeh and other parts of Lebanon, has escalated the conflict between Israel and Hezbollah.

The escalation has sharply increased fears the conflict could spin out of control, potentially drawing in Iran, Hezbollah’s principal backer, as well as the United States.