World leaders expressed deep concern on Tuesday over the potential for a broader conflict following Lebanon's deadliest day in two decades due to Israeli air strikes on Hezbollah strongholds. After nearly a year of cross-border fire since the Gaza war began, Israeli bombardment on Monday resulted in the deaths of 558 people in Lebanon, including 50 children, according to the country's health ministry. This toll, the highest since Israel and Iran-backed Hezbollah fought in mid-2006, heightened fears of a full-scale war engulfing the Middle East.

UN Secretary-General Antonio Guterres was "gravely alarmed by the escalating situation...and the large number of civilian casualties, including children and women," his spokesman Stephane Dujarric stated. "Tens of thousands of people were forced from their homes yesterday and overnight, and the numbers continue to grow," said United Nations refugee agency spokesman Matthew Saltmarsh in Geneva.

Israel's closest ally, the United States, urged against any Israeli ground invasion targeting Hezbollah. "We obviously do not believe that a ground invasion of Lebanon is going to contribute to reducing tensions in the region, to preventing an escalatory spiral of violence," a senior US official said Monday on condition of anonymity.

EU foreign affairs chief Josep Borrell warned on Monday that "We are almost in a full-fledged war." He added, "We're seeing more military strikes, more damage, more collateral damage, more victims...Everybody has to put all their capacity to stop this."

Iran's President Masoud Pezeshkian told CNN, "We must not allow Lebanon to become another Gaza at the hands of Israel." He also noted, "Hezbollah cannot stand alone against a country that is being defended and supported and supplied by Western countries, by European countries and the United States."

China's top diplomat Wang Yi stated, "We pay close attention to developments in the region, especially the recent explosion of communications equipment in Lebanon, and firmly oppose indiscriminate attacks against civilians." Foreign ministry spokesman Lin Jian later expressed Beijing's "deep shock by the relevant military actions that have caused a large number of casualties."

Jordan's King Abdullah II urged the international community to act to stop the "danger of Israeli escalation" in Lebanon and "protect innocent civilians...before the region is dragged into a comprehensive regional war." In a phone call with Lebanese caretaker Prime Minister Najib Mikati, the king emphasized that "stopping the escalation in the region begins with an immediate end to the war on Gaza."

Qatar, a key mediator in talks to reach a Gaza truce, condemned the Israeli aggression on Lebanon, stating that the escalation "puts the region on the brink of the abyss and exposes it to more tensions." Russia called the strikes "an event that is potentially very dangerous," risking the expansion of the conflict and "complete destabilisation of the region," according to Kremlin spokesman Dmitry Peskov.