Lebanon said 51 people were killed and more than 220 injured in Israeli strikes Wednesday, including two rare strikes in mountain areas outside Hezbollah's traditional strongholds in the south and east.

An Israeli strike on the village of Joun in the Chouf mountains, southeast of Beirut, killed at least four people.

Prime Minister Benjamin Netanyahu vowed Tuesday that the Israeli military would press on with its aerial bombing campaign against Hezbollah, as Israeli jets pounded Lebanon.

"We will continue to hit Hezbollah... the one who has a missile in his living room and a rocket in his home will not have a home," Netanyahu said in a statement after visiting an Israeli intelligence base.

U.S. President Joe Biden on Tuesday urged a diplomatic solution as Israel strikes Hezbollah targets, warning against a "full-scale war" in Lebanon.

"Full-scale war is not in anyone's interest. Even though the situation has escalated, a diplomatic solution is still possible," Biden said in an address to the UN General Assembly.

Lebanon on Tuesday extended the closure of schools, universities and nurseries until the end of the week as Israeli strikes continued on east and south Lebanon and Beirut's southern suburbs.

"The closure of public and private schools" including high schools, as well as vocational institutes and universities, "is extended until the end of this week", Education Minister Abbas Halabi said in a statement. The health ministry also announced the closures of nurseries across the country until the end of the week.

Hezbollah urged Lebanese to discard Israel leaflets dropped over the country's east on Tuesday, warning against scanning barcodes that it said could compromise personal data.

"The Zionist enemy is dropping leaflets with barcodes in the Bekaa region and may drop them elsewhere," the Iran-backed group said in a statement.

United Nations Secretary-General Antonio Guterres warned world leaders gathering in New York that Lebanon was on the "brink," a day after 558 people were killed by Israeli strikes there.

"We should all be alarmed by the escalation. Lebanon is at the brink," Guterres said at the opening of the UN's signature annual event.

World leaders on Tuesday sounded the alarm over fears of a wider war after Lebanon suffered its 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 erupted, Israeli bombardment on Monday killed 558 people in Lebanon, including 50 children, according to the country’s health ministry.

A Lebanese security source said an Israeli strike hit Hezbollah's south Beirut stronghold Tuesday, with the Israel army confirming it carried out a "targeted" strike in Beirut's southern suburbs.

At least six people were killed and 15 others wounded in the strike, the Health Ministry said.

Some 500 people have crossed from Lebanon to war-torn Syria, a Syrian security official told AFP Tuesday, fleeing the deadliest Israeli bombardment since Hezbollah and Israel fought a devastating war in 2006.

"Around 500 people crossed the border through the Qusayr and Dabousiya crossings between 4 pm (1300 GMT) and midnight," Monday, the security official told AFP, requesting anonymity to discuss sensitive matters. "Vehicles were still crossing in the early hours of the morning," he added.

The Kremlin said Tuesday that the escalation of the conflict between Israel and Lebanon's Hezbollah risked completely destabilizing the region.

"It is, of course, an event that is potentially very dangerous," risking expansion of the zone of the conflict and "complete destabilization of the region", Kremlin spokesman Dmitry Peskov told journalists.