An airstrike has leveled an apartment building and killed three Palestinian militants in central Beirut, as Israel appeared to send a clear message that no part of Lebanon is out of bounds.

Israel bombed the center of Beirut for the first time in almost a year of hostilities with Lebanon’s Hezbollah, as the military steps up air assaults following the killing of the Iran-backed group’s chief last week.

Hezbollah leader Hassan Nasrallah, who led the terror group for more than 30 years, was killed in an Israeli airstrike. Nasrallah, 64, was killed during a massive airstrike on the Iran-backed group's "central headquarters" in Beirut, Lebanon on Friday, the Israel Defense Forces said in a statement.