"Iran threatens vengeance" over the the assassination of Hezbollah's chief Hassan Nasrallah, reads the front page of The Observer. Ayatollah Ali Khamenei promises his death will "not go unavenged", as his country holds five days of official mourning.

Israeli Prime Minister Benjamin Netanyahu has issued a fresh warning to Iran, saying there was no place in the Middle East beyond Israel's reach amid a flurry of strikes against Hezbollah in Lebanon.

The first apparent Israeli airstrike on central Beirut in nearly a year of conflict struck an apartment building early Monday, killing three members of a Palestinian faction.