Israel rejected proposals on Thursday for a ceasefire with Hezbollah, defying calls from allies including the United States for a halt in fighting.

Israeli warplanes bombarded Lebanon, including a strike on the southern suburbs of Beirut that shook the capital. On its own side of the border, the Israeli army staged an exercise simulating a ground invasion.

The relentless pressure on Iran-backed Hezbollah in Lebanon, including intense airstrikes and assassinations of some of its senior commanders, raised concern that of a wider war spreading across the region.

The military, which has vowed to secure Israel's northern border and return thousands of Israeli citizens to communities there, said the exercise of its 7th brigade took place a few kilometres from the Lebanese border.

Shortly afterwards the military said it was carrying out "precise strikes" in Beirut. The sound of a blast was heard and smoke seen rising in the southern suburbs, a Hezbollah stronghold. The attack targeted a senior Hezbollah leader whose fate was not immediately known, a security source told Reuters.

The strike hit near a part of the southern suburbs where many civilians also live and work.

"There will be no ceasefire 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 Lebanese Prime Minister Najib Mikati had expressed hope that a ceasefire could be reached soon.

Asked about Israel's rejection of a U.S.-backed Lebanon ceasefire proposal, US Secretary of State Antony Blinken said: "The world is speaking clearly for virtually all of the key countries in Europe and in the region on the need for the ceasefire."

He added that he would be meeting with Israeli officials in New York later on Thursday.

Hundreds of thousands of people have fled their homes seeking safety in the face of the heaviest Israeli bombardment of Lebanon since a major war in 2006. World leaders have voiced concern that the war - running in parallel to Israel's war in Gaza - was escalating rapidly.

The United States, France and several other allies called for an immediate 21-day ceasefire across the Israel-Lebanon border. They also expressed support for a ceasefire 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.

More than 600 people in Lebanon have been killed since Monday in Israel's strikes on Lebanon.

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 ceasefire 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.

Israeli fighter jets on Thursday hit infrastructure on the Lebanese-Syrian border to stop the transfer of weapons from Syria to Hezbollah in Lebanon, Israel's military said.