Israel rejected on Thursday a proposal for a cease-fire in Lebanon, defying calls from allies like the U.S. for an immediate three-week pause to prevent a broader conflict.

"There will be no cease-fire in the north," Foreign Minister Israel Katz said on X. "We will continue to fight against the Hezbollah terrorist organization with all our strength until victory and the safe return of the residents of the north to their homes."

The comments dashed hopes for a swift settlement after Prime Minister Najib Mikati had expressed hope that a cease-fire could be reached soon in Lebanon, where hundreds of thousands of people have fled their homes seeking safety.

World leaders voiced concern that the conflict – running in parallel to Israel's war in Gaza – was escalating rapidly.

Israel carried out some of the heaviest attacks in nearly against the Iran-backed Hezbollah group while raising fears of a new Israeli ground offensive across the Lebanese-Israeli frontier.

Hezbollah has faced off against the Israeli military since the movement was created by Iran's Revolutionary Guards in 1982 to counter an Israeli invasion of Lebanon. It has since evolved into Tehran's most powerful Middle East proxy.

The United States, France and several other allies called for an immediate 21-day cease-fire across the Israel-Lebanon border. They also expressed support for a cease-fire in Gaza following intense discussions at the United Nations.

Israeli Prime Minister Benjamin Netanyahu, heading to New York to address the U.N., said he had not yet given his response to the truce proposal but had instructed the army to fight on. Hardliners in his government said Israel should reject any truce and keep hitting Hezbollah until it surrenders.

Israel has launched the heaviest air strikes against Lebanon since a 2006 war over the past week, killing more than 600 people, as months of cross-border fire with the Iranian-backed Hezbollah movement spiraled close to all-out war.

Hezbollah has fired hundreds of missiles at targets in Israel including, for the first time, its commercial hub Tel Aviv, although Israel's aerial defence system has ensured that the damage has been limited.

Asked if a cease-fire could be secured soon, Lebanese leader Mikati told Reuters: "Hopefully, yes." His caretaker administration includes ministers chosen by Hezbollah, widely seen as Lebanon's most powerful political force.

On Wednesday, Israel's army chief made the most explicit public comment yet on the possibility of a ground assault on Lebanon, telling troops near the border to be prepared to cross.

An Israeli strike hit a border crossing between Lebanon and Syria on the Syrian side, said Lebanon's transport minister.

At least 23 Syrians, most of them women and children, were killed when Israel hit a three-story building in the Lebanese town of Younine overnight, the town's mayor, Ali Qusas, told Reuters. Lebanon is home to around 1.5 million Syrians who fled civil war there.

Sheltering in schools

Thousands of Lebanese have sought shelter in schools in Beirut. In one of them, women could be seen leaning out of classroom windows, smoking cigarettes or airing out foam mattresses they had slept on this week.

"I just want to know if there will be a little electricity at night so I can go buy a fan," one woman said.

Aid organizations were distributing clothes and food, and checking on any medications needed by elderly people who had fled too quickly to bring their prescriptions with them.

The Israeli military said it had attacked dozens of Hezbollah targets including fighters, military buildings and weapons depots, in several areas Thursday morning.

Around 45 projectiles were fired from Lebanon toward the western Galilee area, some of which were intercepted with the rest falling on open ground, said the Israeli military.

The relentless fighting has led some neighboring countries to worry about the safety of their citizens living in Lebanon. Türkiye is making preparations for the possible evacuation of its citizens and foreign nationals from Lebanon, a Turkish Defense Ministry source said Thursday.

Israel has made a priority of securing its northern border and allowing the return there of some 70,000 residents displaced by near-daily exchanges of fire, which Hezbollah initiated a year ago in solidarity with the Palestinian resistance group Hamas in Gaza.

Israel's airstrikes sharply intensified since Monday, when more than 550 people were killed in Lebanon's deadliest day since the end of a 1975-1990 civil war.

The bombing follows attacks last week when pagers and walkie-talkies exploded across Lebanon, killing scores of people and wounding thousands including Hezbollah members.