Hezbollah said it had fired a ballistic missile at the Israeli city of Tel Aviv on Wednesday, with the Israeli military describing the launch as unprecedented.
Sirens sounded in Tel Aviv following the launch, the Israeli military said, adding that it had intercepted a "surface-to-surface missile" over the city.
It is the first time Hezbollah has claimed a ballistic missile strike since its nearly year-long battle with Israel began after its Palestinian ally Hamas carried out its October 7 attack.
An Israeli military spokesman told AFP it was also "the first time ever" a Hezbollah missile had reached the Tel Aviv area.
In south Lebanon, a stronghold of Hezbollah, Israeli warplanes bombed villages for a third day on Wednesday, after air raids earlier this week killed at least 558 people in the deadliest day of violence since the 1975-1990 civil war.
Lebanon's National News Agency said the overnight raids caused more casualties, with officials saying hundreds of thousands of civilians have fled their homes to escape the sharp escalation in violence between Hezbollah and Israel.
The United Nations Security Council said it will hold an emergency meeting on the crisis in New York on Wednesday, while UN Secretary-General Antonio Guterres warned the situation was critical.
Nour Hamad, a 22-year-old student in the Lebanese city of Baalbek, described living "in a state of terror" all week.
"We spent four or five days without sleep, not knowing if we will wake up in the morning," she said.
"The sound of the bombardment is very frightening, everyone's afraid. The children are afraid, and the grown-ups are afraid too," she said.
Longtime foes Hezbollah and Israel have been locked in near-daily exchanges of fire since Hamas's October 7 attack on Israel.
The attack sparked a war in Gaza that has drawn in ally Hezbollah and other Iran-backed armed groups from across the Middle East, including Yemen and Iraq.
Lebanese Health Minister Firass Abiad said the "vast majority, if not all" of the 558 people killed in Israel's aerial bombardment on Monday were unarmed civilians in their homes.
- Rocket commander killed -
Hezbollah claimed 18 attacks on Israel on Tuesday, while the Israeli military said the Iran-backed group fired about 300 rockets across the border.
Hezbollah also confirmed an Israeli claim that it had killed their rocket forces commander Ibrahim Kobeissi in a strike on the Lebanese capital.
Early Wednesday, a Lebanese security source said a new Israeli strike hit the Saadiyat area near Beirut, with a "warehouse" targeted.
At the UN General Assembly in New York, Secretary-General Guterres issued a stark warning.
"We should all be alarmed by the escalation. Lebanon is at the brink," he said, while cautioning against "the possibility of transforming Lebanon (into) another Gaza".
US President Joe Biden, whose government is Israel's main backer, warned against a full-blown war in Lebanon in his speech during the New York gathering.
"Full-scale war is not in anyone's interest. Even though the situation has escalated, a diplomatic solution is still possible," Biden said.
Lebanon's foreign minister, also at the UN assembly, said the number of displaced Lebanese had soared to nearly 500,000 since Israel ramped up its military campaign.
A security official in neighbouring Syria told AFP about 500 people had crossed the border to flee the bombing.
- Defiant Netanyahu -
Israeli Prime Minister Benjamin Netanyahu delayed his departure for New York until Thursday, where he too is due to speak at the General Assembly.
"During the day, the prime minister will hold consultations to discuss the continuation of the attacks in Lebanon," his office said.
Netanyahu defied international calls for restraint, vowing on Tuesday to keep up its campaign against Hezbollah.
"We will continue to hit Hezbollah... the one who has a missile in his living room and a rocket in his home will not have a home," he said.
Iran, Hezbollah's main backer, condemned Israel's raids, with its president, Masoud Pezeshkian, saying its ally "cannot stand alone".
"We must not allow Lebanon to become another Gaza at the hands of Israel," he said.
- 'New phase' -
While the Israel-Lebanon border has seen near-daily clashes for a year, the violence escalated dramatically last week, when coordinated communications device blasts that Hezbollah blamed on Israel killed 39 people and wounded almost 3,000.
Then Israel carried out an air strike on Hezbollah's south Beirut stronghold, killing a top military commander and other fighters and civilians.
Efforts to end the war in Gaza, which analysts say are key to stopping the escalation in Lebanon, remain stalled.
The war in Gaza began with Hamas's October 7 attack on Israel, which resulted in the deaths of 1,205 people, mostly civilians, according to an AFP tally based on Israeli official figures that include hostages killed in captivity.
Of the 251 hostages seized by militants, 97 are still held in Gaza, including 33 the Israeli military says are dead.
Israel's retaliatory military offensive has killed at least 41,467 people in Gaza, most of them civilians, according to figures provided by the Hamas-run territory's health ministry. The UN has described the figures as reliable.