Israel said it does not want war in Lebanon but could send its neighbour "back to the Stone Age", as the UN's humanitarian chief warned such a conflict would be "potentially apocalyptic".
The border between the two countries has seen daily exchanges of fire between Israeli forces and Iran-backed Hezbollah militants ever since the October 7 attack on Israel by Hezbollah's ally Hamas, which triggered the war in Gaza.
Fears those exchanges could escalate into full-blown war have only grown in recent weeks as cross-border attacks intensified, and after Israel revealed it had approved plans for a Lebanon offensive, prompting new threats from Hezbollah chief Hassan Nasrallah.
Israeli Defence Minister Yoav Gallant said during a visit to Washington on Wednesday that his country could "take Lebanon back to the Stone Age, but we don't want to do it".
"We do not want war, but we are preparing for every scenario," he told reporters.
"Hezbollah understands very well that we can inflict massive damage in Lebanon if a war is launched."
Israel's allies, including key defence backer the United States, have been keen to avoid such an eventuality. A US official said Washington was engaged in "fairly intensive conversations" with Israel, Lebanon and other actors, and believed that no side sought a "major escalation".
US Defense Secretary Lloyd Austin told Gallant on Tuesday that another war with Hezbollah could have "terrible consequences for the Middle East", and urged a diplomatic solution.
Germany on Wednesday, echoing a Canadian warning from the day before, "urgently requested" its citizens in Lebanon leave the country.
"The current heightened tensions in the border area with Israel could escalate further at any time," updated foreign ministry advice in Berlin said.
UN humanitarian coordinator Martin Griffiths told reporters in Geneva on Wednesday that Lebanon was "the flashpoint beyond all flashpoints".
"It's beyond planning. It's potentially apocalyptic," warned Griffiths, whose term ends this week.
A war involving Lebanon "will draw in Syria... it will draw in others", he added. "It's very alarming."
Lebanon's national news agency reported about 10 Israeli strikes on areas near the border on Wednesday, including one around 10:00 pm that destroyed a building in Nabatiyeh, wounding five people.
There was no immediate comment from the Israeli military on the strike.
Hezbollah on Wednesday claimed six attacks against Israeli military positions in the border region.
- Relative calm -
As Israel's war against Hamas in the Gaza Strip nears its 10th month, bombardments in the besieged Palestinian territory appeared to ease after Israeli Prime Minister Benjamin Netanyahu said the "intense phase" of Gaza operations was winding down.
Some of those forces would likely then be redeployed to the Lebanese border -- but "primarily for defensive purposes", according to the PM.
US officials including Secretary of State Antony Blinken have voiced hope that a ceasefire in Gaza could lead to a reduction in hostilities on the Lebanese border as well.
During the night from Wednesday to Thursday, witnesses reported bombings in areas around the Gaza Strip, and fighting had raged earlier Wednesday between Israeli troops and Palestinian militants in Gaza's southern city of Rafah.
The civil defence agency and medics said at least four people, including three children, were killed in a strike Wednesday on a house in Beit Lahia, in the north.
However, agency spokesman Mahmud Basal told AFP "there have been almost no attacks" and "the rest of the areas in the Gaza Strip are calm compared to yesterday".
The bloodiest ever Gaza war started with Hamas's October 7 attack on southern Israel, which resulted in the deaths of 1,195 people, mostly civilians, according to an AFP tally based on Israeli figures.
The militants also seized about 250 hostages, 116 of whom remain in Gaza although the army says 42 are dead.
Israel's retaliatory offensive has killed at least 37,718 people, also mostly civilians, Hamas-run Gaza's health ministry said.
The deaths include 10 members of Qatar-based Hamas political chief Ismail Haniyeh's family, including his sister, who Palestinian officials said were killed on Tuesday.
The war has triggered a humanitarian crisis in the besieged territory, with hospitals struggling to function, and food and other essentials hard to come by.
Philippe Lazzarini, head of the UN Palestinian refugee agency UNRWA, warned Tuesday of the war's dire impact on children.
"We have every day 10 children who are losing one leg or two legs on average," Lazzarini told reporters, adding "that means around 2,000 children after the more than 260 days of this brutal war".
In Cyprus, USAID officials said just 1,000 tonnes of the 7,000 tonnes of aid shipped to Gaza had been distributed because of looting and security problems.