By Jessica Frank-Keyes Israel launched a wave of air strikes across southern Lebanon early on Sunday in what it said was a pre-emptive strike on Hezbollah. It came as the militant group said it had launched hundreds of rockets and drones to avenge the killing of one of its top commanders last month. The heavy exchange of fire threatened to trigger an all-out war that could draw in the United States, Iran and militant groups across the region. It could also torpedo efforts to forge a ceasefire in Gaza, where Israel has been at war with the Palestinian group Hamas, an ally of Hezbollah, for more…