BEIRUT—Six Shi’ites were shot dead in Beirut on Thursday, in an attack on supporters of Hezbollah and its ally who were gathering to demand the removal of the judge investigating the explosion that ripped through the city’s port last year. The shooting, which took place on a front-line of Lebanon’s 1975–90 civil war and evoked scenes reminiscent of that conflict, marks the deadliest civil violence in Beirut since 2008. It also highlights a deepening crisis over the probe into the catastrophic August 2020 explosion that is undermining government efforts to tackle one of the most dramatic economic meltdowns in history. The Iran-backed Hezbollah and its ally, the Shi’ite Amal Movement, accused the Lebanese Forces (LF), a Christian party that has close ties to Saudi Arabia, of mounting the attack. Interior Minister Bassam Mawlawi said snipers had opened fire and aimed at people’s heads. The LF denied any involvement and condemned …