Israel agreed to test how it might execute a military withdrawal from Lebanon, under a U.S.-brokered agreement between the two countries unveiled on Friday by Secretary of State Marco Rubio.

Speaking at the State Department, Mr. Rubio said the two countries — which committed months ago to the goal of striking a lasting peace and security deal — had struck a new “framework agreement” to that end after several days of meetings.

Tensions have risen between the Trump administration and both countries about whether Lebanon’s fate will be linked to U.S. peace negotiations with Iran. The agreement reached on Friday amounts to a statement by the United States, Israel and Lebanon that they intend to shape Lebanon’s future independent of the U.S.-Iran conflict.

While Mr. Rubio praised the agreement as a “major milestone,” in remarks to reporters he acknowledged that it marks only “the beginning of the beginning” of negotiations between Israel and Lebanon, adding that “there’s a lot of work ahead.”

The challenges of reaching an enduring pact that would be upheld by the various interested parties appeared to compound on Friday, as retaliatory strikes by the United States on Iranian missile and drone sites left a cease-fire between the two countries in doubt.

The centerpiece of the agreement between Israel and Lebanon is a plan for Israel’s military to withdraw from a small fraction of occupied territory in southern Lebanon, which is home to the Iran-backed proxy group Hezbollah. Israel is waging its most sustained war in years against the militant group.

The limits of the agreement were reflected by a statement from Prime Minister Benjamin Netanyahu of Israel. He emphasized not the modest territory Israel says it will give up, but instead the much larger swath of Lebanon that it will continue to occupy.

“The most important thing is that, first and foremost, Israel remains in the security zone in southern Lebanon,” Mr. Netanyahu said. “This is a major achievement, and we will maintain it as long as Hezbollah has not been disarmed, as long as there is a threat to the State of Israel.”

A Hezbollah official, who spoke to the news media on the condition of anonymity, said the group rejected the framework agreement. The official said that the plan effectively allowed Israel’s continued presence in southern Lebanon and that Hezbollah would not give up its weapons without an Israeli withdrawal, echoing its longtime stance.

The plan would begin to establish “pilot zones,” in which Israel’s military would yield control to the Lebanese Armed Forces, who would then be responsible for ensuring Hezbollah did not re-emerge there.

Mr. Netanyahu said the Israel Defense Forces recommended the two areas, one on each side of Lebanon’s Litani River.

But the Israeli leader did not offer a timeline for the withdrawal, saying only that Israel would allow the Lebanese army to “begin organizing” to take control of the areas.

Israeli officials remain deeply skeptical about the prospect of expanding the pilot zones, arguing that the Lebanese army lacks the training, equipment and political will to defang Hezbollah.

The long-term goal of the trilateral talks, which began this spring, is a peace agreement with Israel in which Lebanon’s government fully disarms Hezbollah and takes control of areas in southern Lebanon from which the group attacks Israel.

In return, Israel would end its attacks against Hezbollah targets in Lebanon, which have included heavy airstrikes on the capital of Beirut and high civilian casualties, and ultimately withdraw entirely from the country.

Iran insists that Israel’s military campaign against Hezbollah — which Israel calls self-defense against the group’s cross-border missile and rocket attacks — must end immediately and completely, and that Israel must withdraw from Lebanese territory.

Many Israeli and Lebanese officials were unnerved by language in a memorandum of understanding signed by Iran and the Trump administration earlier this month stating that a final peace deal between the United States and Iran would ensure “the permanent termination of the war on all fronts, including in Lebanon.”

Israel adamantly rejects any linkage between Lebanon and Mr. Trump’s talks with Iran. That has caused friction between Mr. Trump and Mr. Netanyahu as the American president has sought to sustain fragile diplomacy with Iran and restore free shipping through the Strait of Hormuz.

Lebanese officials opposed to Hezbollah fear that Mr. Trump might make concessions to Iran that would allow its continued influence in Lebanon.

Lebanon’s government announced plans last fall to disarm Hezbollah, a move that some of the country’s leaders fear could trigger a new civil war. But it has made little progress toward that goal.

And now officials in Beirut fear the tide may be turning, said Firas Maksad, the managing director for the Middle East and North Africa practice at Eurasia Group.

“The government has shifted from an offensive posture toward Hezbollah to now very much being on the defensive and feeling quite undermined — especially by an American understanding with Tehran linking Lebanon’s fate to Iran,” he said.

Israel and Lebanon also agreed to create a military coordination group facilitated by the United States, Mr. Rubio said in his statement. He added that the United States was committing $100 million in humanitarian assistance to Lebanon, in coordination with the United Nations.

Mr. Maksad noted that Israel and Lebanon had many issues to resolve, including whether and how the Lebanese Armed Forces could take over for Israel’s military in occupied areas that have a strong Hezbollah presence. But for now, he said, Friday’s agreement suggested a determination to stand up to Iran.

“Despite growing fears that Iran and Hezbollah are now emboldened by the outcome of the Iran war, by signing on to an understanding with Israel, authorities in Beirut are signaling determination to maintain their role, not allowing Iran to dictate in Lebanon,” he said.

Mr. Netanyahu also emphasized that message.

“Iran has been trying to force us, through pressure, to withdraw from southern Lebanon,” he said. “In effect, Israel, Lebanon and the United States are telling them: This is none of your business. You have no role in Lebanon.”

Lia Lapidot and Hwaida Saad contributed reporting.