BEIRUT—An Israeli airstrike targeted Hassan Nasrallah, who for more than three decades has commanded Hezbollah as a fierce Islamist backed by Iran, leading its transformation into the world’s most heavily armed nonstate force.

Israel on Friday sought to deal a decisive blow to Hezbollah by targeting the Iranian-backed group’s long-time leader Hassan Nasrallah, underscoring its willingness to escalate warfare in the region to achieve its aims.

"Israel may achieve tactical achievements in its military operations, but it loses the strategic battle," a Hamas official said.