Israel was on alert Thursday after its arch foe Iran threatened reprisals over a strike in Syria this month that killed two Iranian generals, and as the war on Gaza ground on. Days after Israel strengthened its air defences and paused leave for combat units, the United States also warned of the risk of an attack by Iran or its allied groups at a time Middle East tensions have soared. Iran is “threatening to launch a significant attack on Israel”, US President Joe Biden said on Wednesday, pledging “ironclad” support for its top regional ally despite diplomatic tensions over Israel’s military co…