Smoke billows over southern Lebanon following an Israeli strike, amid ongoing cross-border hostilities between Hezbollah and Israeli forces, as seen from Tyre, Lebanon, Sept. 25. Reuters-Yonhap

The United States, France and several allies called for an immediate 21-day ceasefire across the Israel-Lebanon border while also expressing support for a ceasefire in Gaza following intense discussions at the United Nations on Wednesday.

The ceasefire would apply to the Israel-Lebanon "Blue Line," the demarcation line between Lebanon and Israel, and would allow the parties to negotiate towards a potential diplomatic resolution of the conflict, a senior Biden administration official said.

"We call on all parties, including the governments of Israel and Lebanon, to endorse the temporary ceasefire immediately," according to a joint statement of the countries released by the White House.

The allies that signed the joint statement included Australia, United Arab Emirates, Saudi Arabia and the European Union.

Israel widened its airstrikes in Lebanon on Wednesday and at least 72 people were killed, according to a Reuters compilation of Lebanese health ministry statements. The ministry earlier said at least 223 were wounded.

Israel's military chief said a ground assault was possible, raising fears the conflict could spark a wider Middle East war.

Over the last several months, Washington has been engaging with officials in Israel and Lebanon to reduce hostilities, the senior White House official said.

"We have had those discussions for quite some time," the official said, adding Washington and its allies were aiming to convert those discussions into a broader agreement during this 21-day ceasefire period.

The official said Biden had been focused on the possibility of a ceasefire "in almost every conversation he had with world leaders" at the United Nations General Assembly this week.

Based on discussions with Israelis and Lebanese, the U.S. and its allies felt this was the right time for a call for a ceasefire, the official added.

Israel's U.N. Ambassador Danny Danon told reporters before a U.N. Security Council meeting on Wednesday that Israel would welcome a ceasefire and preferred a diplomatic solution. He then told the Security Council that Iran was the nexus of violence in the region and peace required dismantling the threat.

Iran's Foreign Minister Abbas Araqchi told reporters before the council meeting that his country supported Hezbollah and would not remain indifferent if the conflict in Lebanon spiraled.

Lebanese Prime Minister Najib Mikati welcomed the call for a ceasefire, saying the key to its implementation is whether Israel is committed to enforcing international resolutions. Asked earlier if a ceasefire could be reached soon, Mikati told Reuters: "Hopefully, yes."

World leaders voiced concern that the conflict — running in parallel to Israel's war in Gaza against Palestinian Hamas militants also backed by Iran — was escalating rapidly as the death toll rose in Lebanon and thousands fled their homes.

Israeli Prime Minister Benjamin Netanyahu was due to arrive in New York on Thursday and address the U.N. General Assembly on Friday.

Mourners carry Hezbollah senior commander Ibrahim Qubaisi's coffin during a funeral for him and Hezbollah commander Hussein Ezzedine, who were killed in Tuesday's Israeli strike on Beirut's southern suburbs, Lebanon, Sept. 25. Reuters-Yonhap

Lebanon conflict puts pressure on Biden, Harris

The U.S. administration has for nearly a year sought unsuccessfully to secure a ceasefire in Gaza.

The conflict has been costly politically for U.S. President Joe Biden and by extension Vice President Kamala Harris' presidential campaign with the violence in Lebanon increasing pressure on his administration to find a diplomatic solution.

Earlier on Wednesday Israel shot down a missile that the Iranian-backed Hezbollah movement said it had aimed at the headquarters of the Mossad intelligence agency near Israel's biggest city, Tel Aviv.

Israeli officials said a heavy missile had headed towards civilian areas in Tel Aviv, not the Mossad HQ, before being shot down.

"You hear the jets overhead; we have been striking all day," General Herzi Halevi told Israeli troops on the border with Lebanon, according to a military statement.

"This is both to prepare the ground for your possible entry and to continue degrading Hezbollah." A Pentagon spokesperson said an Israeli ground incursion did not appear imminent.

As many as half a million people may have been displaced in Lebanon, its foreign minister said. In Beirut, thousands of people displaced from southern Lebanon were sheltering in schools and other buildings.

Lebanon's Prime Minister Najib Mikati, left, attends a Security Council Meeting, Wednesday, Sept. 25, at U.N. headquarters. AP-Yonhap

Israeli airstrikes target Hezbollah leaders

Israeli airstrikes this week have targeted Hezbollah leaders and hit hundreds of sites deep inside Lebanon, where hundreds of thousands have fled the border region, while the group has fired barrages of rockets into Israel.

Mourners thronged a funeral on Wednesday in Beirut's suburbs for two senior Hezbollah commanders killed in Israeli strikes the day before. Fighters in fatigues carried the flag-covered coffins as a band played. The crowd chanted Hezbollah slogans and some wept.

Israel said its warplanes were hitting south Lebanon and the Bekaa Valley, a Hezbollah stronghold further north, and that it was calling up two more reserve brigades for operations on Israel's northern border.

In a video message that made no comment on diplomatic efforts to secure a ceasefire, Netanyahu said Hezbollah was being hit harder than it could ever have imagined.

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 since war broke out in October between Israel and Hamas in Gaza on Israel's southern border.

Lebanese hospitals have filled with the wounded since Monday, when Israeli bombing killed more than 550 people in Lebanon's deadliest day since its civil war ended in 1990. (Reuters)

Israel's Ambassador to the United Nations Danny Danon looks on at the U.N. headquarters in New York City, U.S., Sept. 25. Reuters-Yonhap