Israeli forces battled Hezbollah fighters in Lebanon on Wednesday, with announcing the deaths of eight soldiers, its first combat losses since launching cross-border raids earlier this week, report agencies.
The fighting in two border areas came hours after Iran launched its largest direct attack on Israel to date.
Israeli Prime Minister Benjamin Netanyahu warned Iran would pay for its "big mistake."
Hezbollah's primary backer, Iran, said it would escalate its response if Israel retaliates, defying calls for de-escalation in a war that has cost over 1,000 lives in Lebanon since last week.
At least 1,873 people have been killed and 9,134 injured in Lebanon as a result of Israeli attacks since October 8 of last year, according to a report from the Disaster Risk Management Unit.
Israel shifted its focus last month from the war in Gaza, which erupted after Hamas's October 7 resistance campaign on Israel, to securing its northern border with Lebanon, where it faces Hezbollah.
In Gaza, the civil defence agency said Israeli bombings killed 19 people on Wednesday. Since October 7, Israel's retaliatory military offensive has killed at least 41,689 people in Gaza.
A day after Israel said its troops had started "targeted ground raids" in southern Lebanon, it reported the first death of a soldier in the Israel-Hezbollah war. The toll later rose to eight dead.
Israel bombarded Hezbollah's south Beirut stronghold, having dealt a seismic blow last week by killing the group's leader, Hassan Nasrallah, in a massive strike.
Hezbollah said it forced Israeli soldiers to retreat from a village, targeted an Israeli unit with explosives and destroyed three tanks.
In Beirut, Hezbollah 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 Hezbollah leaders and Iranian Revolutionary Guards killed three 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.
"Iran made a big mistake tonight and will pay for it," Netanyahu said. "Whoever attacks us, we attack them," he added.
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.
President Joe Biden said the United States was "fully supportive" of Israel after the missile attack. After the US backing of Israel in the Middle Eastern conflict, the Pentagon has ordered its nuclear-powered aircraft carrier to remain in the region with a second vessel en route.
on Wednesday, police in Denmark and Sweden said they were probing explosions and gunfire around Israeli embassies in their capitals which took place amid spiralling Middle East tensions.
Meanwhile, UN chief Antonio Guterres called for an end to the "sickening cycle of escalation" in the Middle East.