The U.S., the European Union and almost a dozen other countries have called jointly for an immediate 21-day cease-fire to allow for negotiations between Israel and Hezbollah.

The proposal, outlined late Wednesday, comes after Israel’s military chief urged soldiers to prepare for a potential ground incursion into Lebanon following days of Israeli strikes on its neighbor that have killed more than 600 people and displaced hundreds of thousands.

In a telephone briefing with reporters, senior U.S. administration officials said both parties were going to respond to the proposal. “They are familiar with the text, and again, we’ll let them speak to their actions of accepting the deal in the coming hours,” one of them said.

They added that 21 days “would be a sustained space that was long enough to allow for negotiations on a realistic basis, to be able to reach a complicated agreement.”

Benjamin Netanyahu’s office said he “did not even respond”

But Israeli Prime Minister Benjamin Netanyahu’s office said in a statement that he “did not even respond” to the proposal and had instructed the Israel Defense Forces to “continue the fighting with full force, and according to the plans presented to him.” It added that the fighting in Gaza would “continue until all the goals of the war are achieved.”

The intensifying conflict between the U.S. ally and Iran-backed Hezbollah has fueled fears of a broader regional war.

Israel and Hezbollah, which backs fellow Iranian proxy group Hamas in its ongoing war with Israel, have been engaged in cross-border conflict since Hamas’s Oct. 7 terrorist attack, in which Israeli officials say about 1,200 people were killed. Those exchanges have taken place in parallel with Israel’s assault on the Gaza Strip, which has killed more than 41,000 people according to health officials in the Palestinian enclave.

The violence further intensified in the past week with the deadly explosions of pagers and walkie-talkies across Lebanon, for which Hezbollah blamed Israel, followed by a wave of airstrikes by Israeli forces. Tens-of-thousands of people in both countries have been displaced in the worst violence between them since 2006.

In a joint statement, the countries behind the cease-fire proposal said the situation between Israel and Lebanon “is intolerable and presents an unacceptable risk of a broader regional escalation.”

This is in nobody’s interest

“This is in nobody’s interest, neither of the people of Israel nor of the people of Lebanon,” it said, adding, “It is time to conclude a diplomatic settlement that enables civilians on both sides of the border to return to their homes in safety.”

The proposal was negotiated and agreed to by the U.S., Australia, Canada, the E.U., France, Germany, Italy, Japan, Saudi Arabia, the United Arab Emirates, the United Kingdom and Qatar. It is unclear how Israel and Hezbollah will respond.

In addition to halting the violence between Israel and Hezbollah, officials say, a broader goal of the cease-fire is to jump-start stalled peace talks between Israel and Hamas in Gaza, where at least 97 people kidnapped by Hamas on Oct. 7 are still being held almost a year later.

“We’ll see if it opens up some possibilities on the Gaza side,” one of the senior U.S. administration official told reporters, “because we do need to bring the hostages home, and we remain very focused on that.”

In an appearance Wednesday on ABC’s “The View” before the cease-fire proposal was announced, President Joe Biden said “all-out war” was possible.

“But I think there’s also the opportunity — we’re still in play to have a settlement that could fundamentally change the whole region,” he said.

Shuttle diplomacy

On the sidelines of the United Nations General Assembly this week in New York, Secretary of State Antony Blinken shuttled back and forth among Arab and European countries working on the details of the proposal, a senior State Department official told NBC News.

Blinken first rolled out the broad outlines of the plan Monday evening at a meeting of foreign ministers from the Group of Seven nations, the official said, asking them to refrain from pursuing any other measures in the meantime.

On Wednesday, in a meeting with top diplomats from Gulf Arab nations, Blinken stepped outside with Mohammed bin Abdulrahman Al Thani, the prime minister and foreign affairs minister of Qatar, to secure his country’s support. At the end of the meeting, the official said, Blinken approached Faisal bin Farhan Al Saud, the foreign minister of Saudi Arabia, to ask that the kingdom also sign on to the agreement.

Speaking ahead of the meeting, Blinken had warned that the “risk of escalation in the region is acute.”

Meanwhile, his deputy chief of staff, Tom Sullivan, met with officials from Britain, France, Germany and Italy to get their signoff on the proposal.

French Foreign Minister Jean-Noël Barrot said Wednesday that the cease-fire would allow time for further negotiations and called on both parties “to accept it without delay.”

The Biden administration has also been communicating with Israel and indirectly with Hezbollah throughout the week. Blinken and senior Biden adviser Amos Hochstein met with Lebanese Prime Minister Najib Mikati on Wednesday, and Blinken is expected to meet Thursday with Ron Dermer, a senior adviser to Israeli Prime Minister Benjamin Netanyahu.

Danny Danon, the Israeli ambassador to the U.S., said Netanyahu would arrive in New York on Thursday and address the General Assembly on Friday morning. The Israeli leader is not, however, expected to meet with U.N. Secretary General António Guterres, Danon said.

As NBC News reported earlier this week, Guterres and Netanyahu have not spoken since the Oct. 7 attack, when Guterres’ call to Netanyahu to express solidarity went unanswered and unreturned — an indication of just how much the relationship between Israel and the U.N. has deteriorated.

Speaking Wednesday on MSNBC’s “Andrea Mitchell Reports,” Michael Herzog, the Israeli ambassador to the U.S., said Israel was “willing to give diplomacy a chance” but that “if diplomacy doesn’t work, I think we have to resort to other means to change the calculus and return our people to their homes.”

Fears of ground invasion

Since Monday, Israel has dramatically expanded its aerial assault on Lebanon, issuing warnings for civilians to move away from Hezbollah positions. Almost 500 people were killed on Monday alone in the deadliest day of conflict between Israel and Lebanon since their 34-day war in 2006.

Thousands more people have left Lebanon for neighboring Syria, spending hours in traffic jams.

While the Israel Defense Forces said earlier that the campaign would be limited to aerial attacks, on Wednesday, the IDF chief of staff, Lt. Gen. Herzi Halevi, told his troops to prepare for a possible ground operation, which would be Israel’s first in Lebanon since 2006.

An Israeli ground invasion does not appear to be imminent, Pentagon spokesperson Sabrina Singh said Wednesday. She added that the U.S. military is not providing Israel with intelligence support for its current operations in Lebanon.

“When it comes to Lebanon, the U.S. military has no involvement in Israeli operations,” she said.