Fear that months of deadly tit-for-tat violence on the Lebanese border could devolve into an even more devastating conflict peaked this month, after Israel assassinated a senior Hezbollah commander and the militant group retaliated with massive rocket barrages. This week, several countries, including Germany and Canada, warned their citizens to leave Lebanon, citing the threat of worsening hostilities.

The United States has not yet ordered its citizens to evacuate, but this week it sent an amphibious ship, the USS Wasp, carrying Marines trained for evacuations, to the Mediterranean Sea. The Pentagon has declined to comment on any evacuations plans for Lebanon.

Hezbollah, the Iranian-backed Lebanese militant group, political party and ally of Hamas, has repeatedly said that a halt to Israel’s offensive in Gaza is necessary before its fighters stand down. U.S. officials have acknowledged Hezbollah’s terms while suggesting, without providing details, that there may be options for ending the conflict on the Israel-Lebanon border without a Gaza cease-fire.

With talks underway, anxiety has grown in both Lebanon and Israel over the consequences of a war that would almost certainly result in high civilian casualties, after months of fighting that has already displaced nearly 200,000 Lebanese and Israelis on either side of the border.

Such a conflict would probably involve the United States, Israel’s primary military backer, while striking a blow to the Biden administration’s stated goal of preventing hostilities in Gaza from spreading across the Middle East.

U.S. and Israeli officials have stressed their desire for a broad agreement that would remove Hezbollah’s threat to northern Israel and allow tens of thousands of people displaced from the area to return. But analysts said Hezbollah, absent a permanent cease-fire in Gaza, was unlikely to sign on to a deal that constrained its military options.

Draft agreements have called for the group to move heavy weapons away from the Israeli border, while offering reconstruction funds for Lebanon, among other terms, according to Lebanese and European officials and published reports.

“It is impossible that we will stop if the [war] does not stop in Gaza,” a member of Hezbollah’s media office told The Washington Post this week, reiterating the group’s long-held position. “If it stops in Gaza, it stops in the south,” the media representative said, speaking on the condition of anonymity in line with Hezbollah’s rules.

In the event of a temporary truce in Gaza — short of a permanent cease-fire — Hezbollah would reciprocate in Lebanon, “as happened the first time,” the representative said, referring to the group’s decision to halt fire during a one-week pause in Gaza in November. But that does not mean Hezbollah would accept a broader agreement, which “could not be discussed with us before the war in Gaza is stopped,” the representative said. Hasan Nasrallah, Hezbollah’s leader, has repeatedly said the group does not want a war.

The U.S. diplomatic efforts have been led by Amos Hochstein, a top White House energy adviser who in 2022 successfully mediated a maritime deal between Israel and Lebanon. It was a historic agreement that allowed for the demarcation of maritime borders between the two countries. Hochstein visited Lebanon this month.

Qatar, which has brokered negotiations between Israel and Hamas, has also been asked by the United States to help mediate in Lebanon, according to a person familiar with the effort who, like others interviewed about the ongoing negotiations, spoke on the condition of anonymity to discuss sensitive diplomacy. Qatar’s role was first reported this week by Lebanon’s Al-Akhbar newspaper.

The Biden administration continues to view a cease-fire in Gaza as a key stepping stone to resolving the crisis in Lebanon. But U.S. officials have also begun exploring backup options to de-escalate tensions, according to officials familiar with the matter.

State Department spokesman Matthew Miller on Tuesday declined to spell out the prospects for a U.S. diplomatic effort succeeding, but said that “we think a diplomatic resolution is possible” and “in the interests of all parties.” A senior U.S. official who briefed reporters Wednesday said there were “openings to advance” diplomacy, while also declining to discuss Washington’s backup planning.

“I’m not going to talk in terms of Plan A, Plan B, Plan C,” said the official.

Comments by Nasrallah after Hochstein’s visit this month suggested that the White House remained focused on the Gaza cease-fire as a solution.

He implied that Hochstein had asked Hezbollah to intervene with Hamas to accept a White House cease-fire plan, a suggestion he dismissed. “To accept what? To accept this solution that offers them a six-week week cease-fire and deprives them of their most important trump cards they have, and then expose them to relentless war,” he said, referring to Hamas’s demand for a permanent end to the conflict.

During a visit to Washington this week, Israeli Defense Minister Yoav Gallant said Israel did not want a war with Hezbollah but was “preparing for every scenario.”

“I have met with Amos Hochstein twice this week. We are communicating intensively. Israel wants to find a solution that will change the security situation in the north,” he said.

“We will not accept Hezbollah troops and military formations on the border with Israel. We will not accept threats to our northern communities,” Gallant said. “We are willing to do everything in our power to protect our people. We don’t want to get into a war because it’s not good for Israel. We have the ability to take Lebanon back to the Stone Age, but we don’t want to do it.”

During his private meetings with officials, Gallant sought to strike fear in the minds of his U.S. counterparts, suggesting that Israel was under threat from Iran and Hezbollah in ways not substantiated by U.S. intelligence assessments, said one official in the room during one of his meetings.

Gallant suggested that Iran may just “randomly start a massive war to destroy Israel, which is a bit over the top and not what the intelligence shows,” said the official.

Heiko Wimmen, project director for Iraq, Syria and Lebanon at the International Crisis Group, said that when it came to the threat of war, “everybody realizes, including the Israelis, that there are limited military options and certainly not good options. I am not sure if anyone believes that a ground invasion is something that at this point is advisable or even feasible.”

Hezbollah is an “opponent of a very different caliber” from Hamas, benefiting from nearly 20 years since the last Israeli incursion into Lebanon to prepare for a similar scenario on its home turf, he said, adding that there are “credible” reports that Hezbollah possesses a tunnel network far more advanced and difficult to strike than the one Hamas built in Gaza. (A Hezbollah spokesman, during an interview with The Post in April, said the group had taught Hamas how to build its tunnels.)

The “general sense is that this is something that has a potential to turn out quite badly. It’s not going to rebuild the deterrence of the IDF very much,” Wimmen said, referring to the Israel Defense Forces. That leaves the possibility that Israel would pursue options short of invasion, including a campaign of airstrikes — a strategy predicated on the notion that enough “pain” could be inflicted on Hezbollah to force the group to stand down.

“That is a risky proposition,” Wimmen said. “You never know where the redline is until you step over it.”

Hezbollah has continued to engage in negotiations with Washington, via Lebanese mediators, despite the ongoing battles in Gaza, a European official in Lebanon said.

But if there’s a temporary truce in Gaza and Hezbollah holds its fire, “the question we are now asking ourselves is: Will Israel decide to stop?” the official said.

The worry is that Israel will continue the targeted killing of Hezbollah members in Lebanon — 338 have been killed in the fighting since October — risking retaliation or a miscalculation that could trigger a war.

It would inevitably embroil the United States, said Maj. Harrison Mann, who resigned from the U.S. Defense Intelligence Agency’s Middle East division last month to protest U.S. support for Israel’s offensive in Gaza.

The United States has provided weapons Israel has already used in Lebanon, and has promised continued support even as its ally weighs an expanded war. At the same time, Biden administration officials say they have privately urged Israel not to be the party that escalates the conflict.

Israel “will not launch the offensive until they are fully confident of America’s support,” he said. “So I think the final trigger for a war of annihilation, in the form of a ground offensive, will be when [Prime Minister Benjamin] Netanyahu perceives he has the green light from the U.S.”

Fahim reported from Istanbul, Hudson from Washington and Dadouch from Beirut. Mohamad El-Chamaa in Beirut and Karen DeYoung and Dan Lamothe in Washington contributed to this report.