Israeli air strikes on Lebanon killed at least 492 people on Monday, including 35 children, the health ministry said, marking the deadliest day of cross-border violence since the Gaza war began.
Arab states strongly condemned Israel for the escalating hostilities with Hezbollah, which have intensified to levels unseen in nearly a year.
The war erupted after Hamas and other Palestinian militants launched the unprecedented October 7 attack on Israel, drawing in Hezbollah and other Iran-backed groups.
Israel said it killed a "large number" of Hezbollah militants when it hit about 1,600 sites in southern and eastern Lebanon, including a "targeted strike" in Beirut in what the Israeli military called "Operation Northern Arrows".
Hezbollah said Ali Karake, its third-in-command, was alive and had moved to safety after a source said the strike on the capital targeted him.
The group said early Tuesday it had launched "volleys" of missiles at Israeli military sites, after state media reported new raids in eastern Lebanon.
People in Israel's coastal city of Haifa were seen running for cover on Monday when air raid sirens sounded.
Lebanon's health ministry said the strikes killed 492 people, including 35 children and 58 women, and wounded 1,645 others. Health Minister Firass Abiad said "thousands of families" had been displaced.
Explosions near the ancient city of Baalbek in eastern Lebanon sent smoke billowing into the sky.
"We sleep and wake up to bombardment... that's what our life has become," said Wafaa Ismail, 60, a housewife from the southern village of Zawtar.
'Most difficult week for Hezbollah'
Global powers urged Israel and Hezbollah to step back from the brink of all-out war, as the violence shifted from Israel's southern border with Gaza to its northern frontier with Lebanon.
France and Egypt called on the United Nations Security Council to intervene, while Iraq requested an urgent meeting of Arab states on the sidelines of the UN General Assembly in New York.
Israeli army chief Herzi Halevi said the strikes hit combat infrastructure Hezbollah had been building for two decades.
Israeli Defence Minister Yoav Gallant called Monday "a significant peak" in the operation.
"This is the most difficult week for Hezbollah since its establishment –- the results speak for themselves," he said.
"Entire units were taken out of battle as a result of the activities conducted at the beginning of the week in which numerous terrorists were injured."
Prime Minister Benjamin Netanyahu said Israel was acting to change the "security balance" in the north.
Hezbollah wave of rockets
Hezbollah, which has been trading near-daily fire with Israel in support of Hamas, said it was in a "new phase" of confrontation.
The group said it launched rockets at Israeli military sites near Haifa and two bases in retaliation for Israeli strikes on the south and the Bekaa.
The attack came after an Israeli strike on southern Beirut on Friday killed its elite Radwan Force commander, Ibrahim Aqil, and coordinated communications device blasts that Hezbollah blamed on Israel killed 39 people and wounded almost 3,000 on Tuesday and Wednesday.
Since the cross-border exchanges between Israel and Hezbollah began in October, tens of thousands of people on both sides have fled their homes.
An Israeli military official, who cannot be further identified under military rules, said the operation seeks to "degrade threats" from Hezbollah, push them back from the border, and then to destroy infrastructure.
Lebanese Prime Minister Najib Mikati urged the United Nations and world powers to deter what he called Israel's "plan that aims to destroy Lebanese villages and towns".
'Full-fledged war' nearing
US President Joe Biden, whose country is Israel's main ally and weapons supplier, said Washington was "working to de-escalate in a way that allows people to return home safely".
The Pentagon said it was sending a small number of additional US military personnel to the Middle East after thousands were deployed earlier alongside warships, fighter jets and air defence systems.
A US official, speaking on condition of anonymity at the UN General Assembly, said that Washington opposed an Israeli ground invasion targeting Hezbollah and had "concrete ideas" on how to de-escalate the crisis.
G7 foreign ministers said in a joint statement that "no country stands to gain" from escalating conflict, warning of "unimaginable consequences" if a regional war broke out.
EU foreign affairs chief Josep Borrell warned that Israel and Hezbollah were "almost in full-fledged war", ahead of a gathering of world leaders at the United Nations.
UN chief Antonio Guterres was "gravely alarmed" by civilian casualties in Lebanon, his spokesman said.
The United Nations peacekeeping force in south Lebanon warned "any further escalation of this dangerous situation could have far-reaching and devastating consequences".
Qatar, a mediator in Gaza ceasefire talks, said Israel's bombardment of Lebanon "puts the region on the brink of the abyss", while Turkey said the strikes threatened "chaos" and Jordan urged an immediate end to the escalation "before it is too late".
The Palestinian foreign ministry condemned the strikes and ordered Palestinian medical staff in Lebanon to provide support for the wounded.
Iran's newly elected president, Masoud Pezeshkian, accused Israel of seeking "to create this wider conflict".
Hamas's October 7 attack on Israel resulted in the deaths of 1,205 people, mostly civilians, according to an AFP tally based on Israeli official figures that include hostages killed in captivity.
Of the 251 hostages also seized by militants, 97 are still held in Gaza, including 33 the Israeli military says are dead.
Israel's retaliatory military offensive has killed at least 41,455 people in Gaza, most of them civilians, according to figures provided by the Hamas-run territory's health ministry. The UN has described the figures as reliable.
