Lebanon's Iran-backed Hezbollah group said it fired more than 60 rockets at an Israeli military base on Saturday in response to the killing in Beirut of Hamas's deputy leader.
"As part of the initial response to the crime of assassinating the great leader Sheikh Saleh al-Aruri... the Islamic resistance (Hezbollah) targeted the Meron air control base with 62 missiles of various types," the group said in a statement.
The Israel-Lebanon border has seen near-daily exchanges of fire since the Israel-Hamas war broke out on October 7.
Aruri's killing on Tuesday in a Hezbollah stronghold in south Beirut, which a US defence official said was carried out by Israel, has raised fears of escalation.
In a speech on Friday, Hezbollah leader Hassan Nasrallah warned Israel that the group would respond swiftly "on the battlefield" to Aruri's killing.
On Saturday, air raid sirens went off in towns and cities across northern Israel and the Israeli-occupied Golan Heights.
The Israeli military said it had identified around 40 rocket launches from Lebanese territory on Saturday morning and its forces had struck a cell responsible for some of them.
Later on Saturday, Hezbollah claimed further attacks on Israeli troops and positions, with the Israeli army saying it had retaliated.
The Israeli army said it had "struck a series of Hezbollah terror targets" across southern Lebanon including "a launch post, military sites and terrorist infrastructure".
It said its fighter jets struck two Hezbollah military compounds containing significant assets, including one used by the group's surface-to-air missile unit.
It said that earlier in the day a missile had been fired at one of its drones.
Lebanon's state-run National News Agency reported that Israeli bombardments and air strikes hit several southern towns and villages.
One of the strikes hit a house in Sidon district, approximately 25 kilometres (16 miles) from the border, the news agency said.
Hezbollah said five of its fighters were killed on Saturday, without providing further details.
With tensions escalating on the border, EU chief diplomat Josep Borrell was in Lebanon as part of efforts to prevent a wider regional war.
"It is imperative to avoid regional escalation in the Middle East. It is absolutely necessary to avoid Lebanon being dragged into a regional conflict," he told a news conference in Beirut.
Borrell added that he would be travelling to Saudi Arabia next to discuss "a joint EU-Arab initiative" for peace.
Nearly three months of cross-border fire has killed 180 people in Lebanon, including 134 Hezbollah fighters, but also more than 20 civilians including three journalists, according to an AFP tally.
In northern Israel, nine soldiers and at least four civilians have been killed, according to Israeli authorities.
