Hizbollah said it repelled an Israeli infiltration into southern Lebanon on Wednesday, as Israel reported eight soldiers were killed — its first losses since launching cross-border raids this week.
The clashes came hours after Iran launched its largest missile attack yet on Israel, its sworn enemy. Israeli Prime Minister Benjamin Netanyahu warned Tehran would pay for its "big mistake."
Iran, which backs Hizbollah, said it would step up its response if Israel retaliates, defying calls for de-escalation in a war that has cost more than 1,000 lives in Lebanon.
US President Joe Biden ruled out supporting an Israeli strike on Iran's nuclear sites, while Iranian President Masoud Pezeshkian again warned of a "stronger" response, though he stressed Iran was "not looking for war."
Israel, shifting its focus from the Gaza war, is now trying to secure its border with Lebanon so tens of thousands Israelis displaced by nearly a year of exchanges of fire with Hizbollah can return home.
A day after its military said it was conducting "targeted ground raids" in south Lebanon, Israel reported the first death of a soldier in the Israel-Hezbollah war, a toll that later rose to eight dead.
Israel bombarded Hizbollah's south Beirut stronghold, having dealt a significant blow to the group last week by killing its leader, Hassan Nasrallah, in a massive strike.
Hizbollah said it forced Israeli soldiers to retreat, targeted an Israeli unit with explosives and destroyed three Merkava tanks with rockets as they advanced on Maroun Al-Ras village.
The Israeli army said it staged two brief incursions into Lebanon, warning residents to evacuate more than 20 areas.
In Beirut, Hizbollah targets in the southern suburbs were repeatedly bombarded overnight, with AFP correspondents hearing about 20 explosions and seeing smoke billowing over the area.
The Syrian Observatory for Human Rights war monitor said an Israeli strike on a Damascus neighbourhood frequented by Hizbollah leaders and Iranian Revolutionary Guards killed two people.
Hours after Israel announced the start of ground operations in Lebanon, Iran fired some 200 missiles including hypersonic weapons, sending frightened Israeli civilians into shelters.
Israel said it intercepted most of them. Two people were wounded by shrapnel and a school building was damaged.
The Israeli military said several Iranian missiles struck inside air force bases without causing any casualties or damage.
In Jericho in the occupied West Bank, a Palestinian was killed when "pieces of a rocket fell from the sky and hit him," the city's governor Hussein Hamayel said.
"Iran made a big mistake tonight and will pay for it," Israeli Prime Minister Netanyahu said.
"Whoever attacks us, we attack them."
His defence minister, Yoav Gallant, echoed the warning.
"Iran has not learnt a simple lesson — those who attack the state of Israel, pay a heavy price," he said.
Iran's armed forces chief of staff, Major General Mohammad Bagheri, threatened to fire "with bigger intensity" if Israel makes good on its pledge to retaliate.
Iran's Revolutionary Guards said the missiles were fired in retaliation for Nasrallah's killing alongside its Quds Force commander Abbas Nilforoushan, as well as Hamas leader Ismail Haniyeh in a Tehran bombing in July.
Lebanon's disaster management agency said 1,873 people had died since Israel and Hizbollah began trading fire after the Hamas attacks on October 7, displacing hundreds of thousands.
President Joe Biden said the United States was "fully supportive" of Israel after the missile attack.
Pentagon chief Lloyd Austin condemned an "outrageous act of aggression" by Iran, while Biden's National Security Advisor Jake Sullivan told reporters there would be "severe consequences".
The conflict is now expected to escalate, with analyst Jordan Barkin saying: "This will not end well.
"Netanyahu has a long history of fighting back strongly and quickly when provoked. Restraint is not Mr. Netanyahu's strong suit."
But some Israelis expressed fatigue with the war, with Tel Aviv resident Liron Yori, 22, saying: "I feel very, very disappointed. I see where the war's going and I don't feel comfortable with it."
In central Beirut, people were weary and afraid, though some Hizbollah supporters were defiant.
Youssef Amir, displaced from southern Lebanon, said: "I have lost my home and relatives in this war, but all of that is a sacrifice for Lebanon, for Hezbollah."
Iran's missile attack, its second on Israel in six months, triggered widespread global alarm, as well as a spike in world oil prices.
UN chief Antonio Guterres condemned the Iranian attack on Israel, saying they "do nothing to support the cause of the Palestinian people".
The G7 group of rich nations vowed to work together to reduce tensions in the region and said a diplomatic solution was "still possible".
Hizbollah began low-intensity strikes on Israeli troops a day after Hamas staged its October 7 attack on Israel, which resulted in the deaths of 1,205 people in Israel, mostly civilians, according to an AFP tally based on Israeli official figures that include hostages killed in captivity.
Israel's retaliatory military offensive has killed at least 41,689 people in Gaza, the majority of them civilians, according to figures provided by Gaza health ministry. The UN has described the figures as reliable.
In Gaza, the civil defence agency said Israeli bombings killed 19 people on Tuesday.
Agence France-Presse