The Israeli military has carried out air strikes on Hezbollah targets in Tyre in southern Lebanon, after ordering the evacuation of the entire city.
The military told residents that it was "compelled to act forcefully" in Tyre because the Iran-backed armed group was violating a US-brokered ceasefire that began five weeks ago.
Earlier on Wednesday, Lebanese media reported a wave of Israeli strikes across the south and the eastern Bekaa Valley, with four people killed in the towns of Choukine and Nabatieh.
Hezbollah, which has itself accused Israel of breaching the ceasefire, said it was battling Israeli troops north of the Litani river, about 30km (19 miles) from the border.
It came a day after Israel's prime minister announced an expansion of its ground operation following Hezbollah drone attacks on troops occupying part of southern Lebanon and on civilians in northern Israel.
Thick, black columns of smoke painted Tyre's Mediterranean skyline throughout Wednesday.
Residents watched with horror from balconies, filming on their phones, as powerful Israeli air strikes hit the city, which is one of the biggest in southern Lebanon.
In the afternoon, the Israeli military told everyone in Tyre, as well as its Palestinian refugee camps and surrounding villages, to leave immediately and head north of the Zahrani river, about 40km from the border.
It was one of the most sweeping displacement orders of the conflict to date.
Many people living in Tyre, including those already displaced from other parts of southern Lebanon, have nowhere obvious to go.
Rida, 52, owned a cafe near the beach that was destroyed alongside his home in an air strike minutes before the ceasefire started last month.
He previously told the BBC he would never leave Tyre, where he grew up. Now, the feeling is different.
"I went to the port next to the beach and a lot of people are there," Rida said over the phone on Wednesday. "People packed up their stuff. Everyone is scared. I think that they will erase Tyre."
Earlier, the Israeli military told residents of Nabatieh, north-east of Tyre, and several other towns to leave for the second consecutive day.
The evacuation orders came on the heels of a devastating 24-hour period that saw more than 150 Israeli air strikes tear through some 50 towns and villages across southern Lebanon and the Bekaa Valley.
The Lebanese health ministry said at least 31 people were killed on Tuesday, including 15 in the town of Burj al-Shamali, just east of Tyre.
The Israeli military said it targeted Hezbollah "infrastructure sites and terrorists".
Those strikes took place after Israeli Prime Minister Benjamin Netanyahu said he had instructed commanders to "press the pedal even harder" in targeting Hezbollah in response to the group's attacks, including those involving fibre-optic drones.
On Tuesday evening, Netanyahu told a cabinet meeting that Israeli troops were also "deepening" their operation beyond the strip of land they are already occupying in southern Lebanon, which extends 10km from the border in some places.
"[The military] is operating with large forces on the ground and seizing dominant terrain. We are fortifying the security zone to protect the communities of the north [of Israel]," he said.
Hezbollah said on Wednesday that its fighters had clashed with Israeli forces "at point-blank range" in the town of Zawtar al-Sharqiyeh, which is north of the Litani river and just outside the Israeli-declared "buffer zone" in southern Lebanon.
Israeli officials have said Hezbollah's attacks are violating the temporary ceasefire deal between the Israeli and Lebanese governments, which began on 16 April and has been extended twice since then.
The accusation cuts both ways, though, as Lebanese officials have pointed to the Israeli strikes themselves as violations of that same agreement.
The escalation threatens to derail talks aimed at ending the war between the US, Israel and Iran. Iran insists that any deal must also cover Lebanon, but Israel says it reserves the right to continue to fight the threat from Hezbollah.
Lebanon was drawn into the war on 2 March, when Hezbollah launched rockets into Israel in retaliation for an Israeli strike that killed Iran's supreme leader. Israel responded with an air campaign across Lebanon and a ground invasion.
At least 3,213 people have been killed in Lebanon since the start of the war, according to the country's health ministry - its figures do not distinguish between combatants and civilians.
Israel says 23 of its soldiers and four Israeli civilians have been killed over the same period on both sides of the border.
Additional reporting by Angie Mrad
