GEOFF BENNETT: Israel appears to be starting its invasion of Southern Lebanon, but on what U.S. officials believe will be a more limited basis.

Meantime, Israel continues to launch punishing airstrikes across Lebanon, with some that have targeted leaders of militant groups, in addition to Hezbollah.

Nick Schifrin is in Tel Aviv tonight.

NICK SCHIFRIN: Tonight, the drums of all-out war are beating.

Lebanese soldiers have left the border.

Just miles south, Israeli armored vehicles mass.

A U.S. official tells "PBS News Hour" an invasion could be -- quote -- "imminent."

And Israel tonight declared areas near the border closed military zones.

After this afternoon, Defense Minister Yoav Gallant hinted to armored units they could soon invade.

YOAV GALLANT, Israeli Defense Minister (through translator): We will do what needs to be done.

Our aim is to return residents of Northern Israel to their homes.

We will employ all of our capabilities, including your forces and other forces, from the air, the sea and the ground.

NICK SCHIFRIN: For nearly a year, Israeli towns near the border have been empty, threatened by Hezbollah rockets and short-range weapons just over the border.

Israeli officials say they have reduced Hezbollah's ability to strike, shattered the rank-and-file's communication systems and command-and-control, and decapitated the group with the massive strike that a U.S. senator said used 2,000-pound American bombs to kill leader Hassan Nasrallah.

But, today, his surviving deputy, Naim Kassem, warned the group was still ready to fight.

SHEIKH NAIM KASSEM, Hezbollah Deputy Chief (through translator): We will face any possible attack, and we are ready.

If the Israelis decide to enter by land, the resistance forces are ready for a ground engagement.

NICK SCHIFRIN: President Biden today demanded Israel prioritize diplomacy.

QUESTION: Israel may be now launching a limited operation into Lebanon.

Are you aware of that?

Are you comfortable with their plan?

JOE BIDEN, President of the United States: I'm more aware than you might know, and I'm comfortable with them stopping.

We should have a cease-fire now.

Thank you.

NICK SCHIFRIN: But the U.S. is preparing for escalation.

The Pentagon says it's sending additional fighter squadrons and extending an aircraft carrier strike group to bolster deterrence and help defend Israel.

But Israel is on the offense, over the last few days simultaneously attacking in Gaza at Hamas, in Yemen at the Houthis, and in Lebanon at Hezbollah, all backed by Iran, whose residents Prime Minister Benjamin Netanyahu addressed today.

BENJAMIN NETANYAHU, Israeli Prime Minister: There is nowhere in the Middle East Israel cannot reach.

There is nowhere we will not go to protect our people and protect our country.

With every passing moment, the regime is bringing you, the noble Persian people, closer to the abyss.

NICK SCHIFRIN: But, tonight, Lebanese already feel on the precipice.

A million have fled their homes, fearing invasion and all-out war.

Tonight, the Israeli cabinet has met amid all signs of an Israeli incursion into Lebanon, or perhaps multiple Israeli incursions into Lebanon, Geoff, just days ahead of the anniversary of the October 7 terrorist attacks.

GEOFF BENNETT: And, Nick, what more can you tell us about Israel's goals and its thinking about this operation?

NICK SCHIFRIN: The bottom line, Israeli officials say, is that they need to return to 60,000-plus residents who have been displaced from their homes in Northern Israel since October the 8th.

That is the day that Hezbollah opened fire into Israel in support of Hamas.

And Hezbollah Radwan fighters are still so close to the border of Israel they can fire small-range weapons, rocket-propelled grenades, anti-tank missiles into Israeli towns and cities.

Israel says it has been open to a diplomatic solution to that problem, but appears to be running out of patience.

And we are faced with a limited incursion, or, again, perhaps multiple limited incursions, into Lebanon beginning imminently, if not already.

That is a hold operation that Israel will have to do to clear those Hezbollah fighters from the area, go after tunnels that go under the border, and also clear the missiles and rockets from Southern Lebanon.

What happens after that, Geoff, Israeli officials tell me, will be up to the United States to find some kind of diplomatic solution to guarantee that Hezbollah fighters can't remain on that border.

GEOFF BENNETT: Well, on that point, what more are U.S. officials saying about Israel's plans tonight?

NICK SCHIFRIN: U.S. officials are unusually specific about their conversations with Israeli officials tonight.

They say that it appeared as though Israel was planning a larger incursion into Lebanon, and there is now a -- quote -- "new understanding" between Israel and the U.S. to launch this more targeted operation that will focus again on Hezbollah fighters right along the border, with the goal of returning those Israeli residents to their towns.

This would be much smaller than the war in 2006.

But a U.S. official specifically says the U.S. has expressed concern that an operation that is right now designed to be limited by both time and geography could turn into a longer-term operation with larger goals, as has happened to Israel in the past in Lebanon.

And that goes to the diplomacy I referred to, Geoff, that the U.S. will have to find a diplomatic solution to move those Hezbollah fighters back.

Otherwise, U.S. officials were worried that Israel will decide to remain in Southern Lebanon.

GEOFF BENNETT: Well, let's take a step back, Nick.

Give us a sense of how much has changed on the border and in the region in just the last week.

NICK SCHIFRIN: Yes, so much has changed, especially since the death of Hassan Nasrallah, the secretary-general of Hezbollah, who was really the Hezbollah commander in chief, as well as the communicator in chief.

He was the one who made the military decisions.

He was the one whose speeches were watched across the region.

And his death, combined with the death of so many of his military commanders, along with the severing of their communication systems, thanks to those attacks on the pagers and walkie-talkies, has really left the group in disarray, according to Israeli officials and independent analysts I speak to.

It's also scrambled the calculus of Iran.

Nasrallah was the single most important anchor to Iran's Axis of Resistance.

He was very close to the supreme leader, Ali Khamenei, and Hezbollah was the most important deterrence to Israel against an attack on Iran.

And, frankly, Geoff, it's not clear that Hezbollah can really function as that deterrence tonight.

A senior administration official tells me that while the official policy is diplomacy, this is also a -- quote -- "once-in-a-generation opportunity" to rid or at least reduce Hezbollah's influence in Lebanon.

But, Geoff, that is a huge task.

It is not clear there's a partner in Beirut to do that with or there's an easy diplomatic solution to what we have been talking about, pushing Hezbollah back off that board.

GEOFF BENNETT: Nick Schifrin reporting tonight from Tel Aviv.

Nick, thank you.

NICK SCHIFRIN: Thank you.