Hezbollah chief Hassan Nasrallah has been killed, dealing a major blow to the Lebanese group that has been embroiled in cross-border hostilities with Israel for a year.

Hezbollah’s statement came Saturday shortly after the Israeli army said it had killed Nasrallah in an airstrike on Beirut’s southern suburbs – a move that could destabilize Lebanon and spark a regional war.

Nasrallah, who led Hezbollah for more than three decades, is by far the most powerful person killed by Israel in weeks of intense fighting with Hezbollah. The Israeli army said it carried out a precision airstrike on Friday evening as Hezbollah leaders met at their headquarters in Dahiyeh, south of Beirut.

Lebanon’s health ministry said six people were killed and 91 injured in the strikes, which razed six apartment buildings. Ali Karki, the commander of Hezbollah’s Southern Front, and other commanders were also killed, the Israeli army said.

The Gaza-based Palestinian group Hamas condemned Nasrallah’s killing as a “cowardly terrorist act.”

Israel has shifted the focus of its operation from Gaza to Lebanon, where more than 700 people have been killed in heavy bombardments, according to the Lebanese Health Ministry, after cross-border exchanges escalated over the past week. Most Lebanese deaths occurred on Monday, the deadliest day of violence since the 1975-1990 Lebanese civil war.