Israel on Wednesday told troops to prepare for a potential ground offensive against Hizbollah in Lebanon as US President Joe Biden warned that “all-out war is possible” but pushed for a ceasefire deal.

The Israel Defense Forces’ chief of staff Lieutenant General Herzi Halevi told troops that air strikes on Lebanon were not just aimed at “degrading” the militant group but “to prepare the ground for your possible entry”.

“We are preparing the process of a manoeuvre, which means your military boots, your manoeuvring boots, will enter enemy territory, enter villages that Hizbollah has prepared as large military outposts,” he said.

The speech was Israel’s most explicit threat of a ground offensive since it began an intense bombardment of Lebanon from the air three days ago, striking thousands of targets it said were linked to Hizbollah while killing hundreds of people and adding to fears of all-out war.

In a sign of US concern about an escalating Middle Eastern conflict, Biden said on Wednesday that he was “using every bit of energy I have” to try to halt the fighting, in the hope that a “ceasefire in Lebanon” could pave the way to “dealing with the West Bank” and Gaza.

Biden said Arab nations in the region were “willing to make arrangements with Israel and alliances if Israel changes some policies”.

But his language contrasted with Halevi’s call for Israeli troops to prepare to enter Lebanon, in what would be Israel’s first invasion of the country since the two sides fought a 34-day war in 2006.

The IDF chief added: “Your entry into those areas with force, your encounter with Hizbollah operatives, will show them what it means to face a professional, highly skilled and battle-experienced force.”

The IDF said it was calling up two reserve brigades, which would “enable the continuation of combat” against Hizbollah to defend Israeli territory and allow residents of northern Israel displaced by the cross-border conflict — which has been simmering since Hamas’s attack on Israel last October — to return home.

However, Israel has yet to mobilise military reservists on the scale that it did when launched its offensive on Gaza 11 months ago.

Speaking late on Wednesday, Israeli PM Benjamin Netanyahu said the military operation would continue. “I can’t go into detail about everything we do, but I can tell you one thing: We are determined to return our residents in the north safely to their homes,” he said in a short video.

Israeli air strikes have killed more than 600 people this week, including 51 on Wednesday, according to Lebanese authorities. The International Organization for Migration said at least 90,000 people had been displaced in Lebanon by the violence.

Early on Wednesday, sirens sounded in Tel Aviv as Hizbollah fired a ballistic missile on the country for the first time.

Hizbollah said the Qader 1 ballistic missile, more destructive and longer-range than the rockets the group has fired in the conflict, targeted the headquarters of Israeli intelligence agency Mossad on the outskirts of Tel Aviv.

Though intercepted by Israel’s air defences, with no damage or injuries reported, the launch marked one of the militant group’s deepest strike attempts so far and its first aimed at the economic hub of Tel Aviv.

Israel has been bracing for more intense Hizbollah fire after it began heavy raids on the group’s strongholds on Monday, pounding targets it said included the Iran-backed group’s weapons stores, intelligence and command centres. It has also killed several senior commanders in strikes on Hizbollah-held areas of Beirut over the past 10 days.

But on Wednesday, Israeli air strikes pummelled Lebanon with renewed ferocity, expanding the campaign to new regions of Lebanon outside Hizbollah-dominated areas. Many villages were targeted for the first time, such as in Mount Lebanon to the north of Beirut.

Israel has so far carried out attacks across the south and the Bekaa Valley, along Lebanon’s eastern border with Syria, and on Tuesday killed Hizbollah’s missiles division chief Ibrahim Qobeissi in southern Beirut. 

Bekaa, previously a secondary front in Israeli attacks, has been the target of heavy strikes on villages and the outskirts of the region’s major cities including Baalbek and Hermel. 

The strikes have triggered an exodus of residents from southern Lebanon as panicked families, many already displaced from their homes near the border earlier in the war, fled for safer areas. About half were now housed in shelters, the IOM said.

Israel has pledged to continue the military action until 60,000 citizens displaced by months of cross-border fire can return home.

Hizbollah’s barrages have increased in response and the group has fired deeper into Israel. Most of its projectiles have been intercepted by Israel’s air defences, but the group is thought to have large unused stockpiles. One projectile hit an assisted living facility in the northern town of Tsafed on Wednesday, the IDF said, but no injuries were reported.

The Qader 1 is described by the Center for Strategic and International Studies as a medium-range ballistic missile developed in Iran and first tested in 2015. Analysts believe it can carry a 750kg warhead and hit targets 1,600km away.

More than 3,000 people were injured and 37 killed across Lebanon last week when Hizbollah’s communications devices detonated en masse. The group blamed Israel for the assault, though Israel has not directly commented.

Hizbollah said the Mossad command centre it targeted was “responsible for the assassination of leaders and exploding the pagers and walkie-talkies”.

Hizbollah also revealed it used “Fadi” rockets this week for the first time. The rockets — named after a Hizbollah commander killed in 1987 whose brother was also killed by Israel in January this year — have a longer range, at 70km to 100km, than rockets used so far by the group in the fighting since October.

Data visualisation by Steven Bernard and Chris Cook