BEIRUT—As hundreds of thousands of people gathered for the funeral of slain Hezbollah leader Hassan Nasrallah in Beirut on Sunday, its current chief vowed to continue fighting Israel as the group projected its power despite an Israeli offensive that has left it weakened and in disarray.

Hundreds of thousands of people have packed into a stadium in Beirut and nearby streets for the funeral of Hezbollah’s leader, nearly five months after he was killed in an Israeli airstrike on a southern suburb of the capital.

The long-delayed funeral for Hezbollah’s leader Hassan Nasrallah is taking place Sunday, nearly five months after he was killed in a massive Israeli airstrike on the southern suburbs of Beirut.