Youths walk in Khiam, Lebanon, past Hezbollah's mock rockets at the former Israeli-run prison that was destroyed in the 2006 war. (Mahmoud Zayyat/Agence France-Presse via Getty Images)

When Israeli army commanders describe how the next war against Hezbollah could unfold, they often search for words not used in military manuals. The future conflict, they warn, will be “ferocious” and “terrible.”

For both sides, the Israelis fear.

Yet far worse for Hezbollah and the civilians of Lebanon, they promise.

Ten years after Israel and Hezbollah fought a bloody but inconclusive 34-day war that left more than 1,000 soldiers and civilians dead in July and August of 2006, the Lebanese Shiite militant group has been transformed.

Hezbollah is now a regional military power, a cross-border strike force, with thousands of soldiers hardened by four years of fighting on Syrian battlefields on behalf of President Bashar al-Assad. There are 7,000 Hezbollah fighters in Syria, Israeli commanders say.

Hezbollah leader Hasan Nasrallah addresses supporters from a screen during a ceremony marking the 40th day after Hezbollah commander Mustafa Badreddine (picture on banner) was killed. (Aziz Taher/Reuters)

Hezbollah troops have been schooled by Iranian commanders, funded by Tehran and have learned to use, in combat, some of the most sophisticated armaments available, such as fourth-generation Kornet guided anti-tank missiles. They pilot unmanned aircraft and fight alongside artillery and tanks. They have taken rebel-held villages with Russian air support.

More than 1,000 Hezbollah fighters have died, the Israelis say; they do not describe Hezbollah as “demoralized” but “tested.”

“In 2006, Hezbollah fought a guerrilla war. Today, Hezbollah is like a conventional army,” said Elias Hanna, a retired Lebanese army general who teaches at the American University of Beirut.

[In blow to Hezbollah, senior commander killed in Syria]

Israel fought the first Lebanon war in 1982 against the Palestine Liberation Organization, a conflict that saw Israel occupy southern Lebanon and lay siege to Beirut. Hezbollah arose during that war. The second Lebanon war broke out in July 2006 after Hezbollah abducted a pair of Israeli soldiers on the border.

Ten years ago, Hezbollah fired 4,000 short-range, relatively crude rockets at Israel, about 100 a day, killing some 50 Israeli civilians. Today, the group has 100,000 rockets, including thousands of more accurate mid-range weapons with larger warheads capable of striking anywhere in Israel, including Jerusalem and Tel Aviv, according to Israeli army commanders and military analysts in Israel and Lebanon.

Hezbollah poses a far greater threat to Israel than it did 10 years ago. The challenges posed by Islamist militant movement Hamas in the Gaza Strip are almost trivial by comparison, Israeli senior commanders say.

Earlier this year, Israel Defense Forces Chief of Staff Lt. Gen. Gadi Eisenkot called Hezbollah Israel’s “main enemy” now that Iran’s nuclear ambitions may have been delayed by a decade or more.

Whether Hezbollah’s arsenal of rockets and the overwhelming retaliatory response promised by Israel serves as a dual deterrent is one of those questions that can never be answered — but probably keeps commanders on both sides awake at night.

In Israel’s far north, Misgav Am kibbutz sits on a hilltop above the Lebanon border. There is a popular overlook. There is a gift shop for the tour buses.

[How the Syrian revolt went so horribly, tragically wrong]

On a sunny morning, an Israeli army colonel stood on the hill and pointed toward Lebanese villages at his feet.

“You see villas, red tile roofs, summer homes. You don’t see soldiers in uniforms. They don’t wear uniforms. It looks nice and peaceful, right?” said the commander of a paratrooper reserve brigade, who spoke on the condition of anonymity because he is serving on active duty on the Lebanon border.

“I see rocket rooms, weapons caches, underground compounds,” he said. “I can pinpoint to you, below, a house with washing on the line that is a Hezbollah outpost.”

Israeli military leaders say Hezbollah has spent the past decade transforming hundreds of villages in southern Lebanon into covert fire bases with hidden launch pads, many rigged to operate by remote.

In briefings with reporters in Tel Aviv, Israeli military intelligence officers in the past year have begun to show aerial photographs of villages in Hezbollah’s southern stronghold.

A photograph of Muhaybib, a town south of here, is covered with red squares marking the placement of what the Israelis say are command posts, anti-tank positions, tunnels and launch pads. Israel says there are 90 buildings in the village of 1,100 people and that 35 buildings are being used by Hezbollah.

The message is implicit: This is a target list.

The Israeli commanders in Tel Aviv and here on the Lebanon border may be issuing propaganda as a warning to Hezbollah. Both sides do talk to each other through the media, yet there is broad agreement in Washington, Jerusalem and Beirut that another Lebanon war could be devastating, especially for civilians.

“Hezbollah is not a group or a organization or a movement. It’s an army. A big terrorist army,” said the paratrooper commander, who is a veteran of the 2006 Lebanon war. “We understand that people here find themselves in the middle. The next war will be a terrible war. I think they understand, too, that the next war will be different.”

Speaking publicly, the Israeli generals promise that if Hezbollah launches mass strikes against Israeli cities, Israel will be compelled to respond, similarly, with 10 times as much force. The commanders say they cannot allow Israeli cities to face 1,000 Hezbollah rockets a day.

Historians say the 2006 war came as a surprise for both sides. Hezbollah captured two Israeli soldiers at the border, which sparked a sustained aerial and ground war by Israeli forces — and tough resistance by Hezbollah.

Both claimed victory, but neither won. In Israel, the 2006 Lebanon war is widely viewed by Israelis as a military failure. Hezbollah boasted that it had stood toe-to-toe with the most powerful army in the Middle East, but the widespread destruction and civilian deaths were unpopular.

[Israel to launch one of world’s most advanced missile defense systems]

As the 10-year anniversary approached, both Hezbollah and Israel stressed that they do not want another war — even as both declared themselves ready for one.

“Israel knows Hezbollah has missiles and rockets that can strike anywhere in its territory,” the group’s leader, Hasan Nasrallah, said in a speech delivered by video in February.

Nasrallah warned that Hezbollah rockets could strike ammonia plants at the port in Haifa in any future fight, saying that the damage would be equivalent to an atomic bomb and could lead to the deaths of 800,000 people.

“Haifa is just one of many examples,” Nasrallah said. “The leaders of Israel understand that the resistance has the ability to cover the entirety of occupied Palestine with missiles. We must keep this capability because it acts as a deterrent for the third Lebanon war.”

Israeli Prime Minister Benjamin Netanyahu on Tuesday said, “If the quiet is kept, those facing us will enjoy quiet.” Then he warned that Hezbollah aggression would be met by “an iron fist.”

Today, Hezbollah has lost some of its previous luster because of its decision to fight for Assad in a war that became deeply sectarian, Shiite against Sunni.

Going to Syria might have turned Nasrallah from “a hero to a zero” for many in the Arab world, said Sami Nader, director of the Levant Institute for Strategic Affairs.

“But the Syria war also emboldened them and sharpened his military skills,” he said. “Hezbollah may be tempted to engage Israel in what it hopes is a limited war to recover their prestige.”

Simon Abu Fadel, a political analyst in Lebanon, predicts that in the event of war Hezbollah would try to inflict heavy damage on Israeli cities, power plants and airports to degrade national morale.

“In case of a new war with Israel, Hezbollah’s missiles would be painful to Israel,” he said. “However, the damage would be far less than what Israeli airstrikes could do to Hezbollah and Lebanon.”

“It is not a win-and-lose game,” Fadel said. “It is a mutual exchange of bombing and destruction.”

Suzan Haidamous in Beirut contributed to this report.

Read more:

In jab at Iran, gulf Arab states declare Hezbollah a terrorist group

What we know about the mysterious Hezbollah mastermind killed in Syria

As Kerry pushes for coordination with Russia in Syria, others cry foul

Today’s coverage from Post correspondents around the world