A smoke plume billows during Israeli bombardment on the village of Kfarshuba in south Lebanon on Wednesday. AFP

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 fighters 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".

A damaged Israeli military position targeted by Hezbollah fighters is seen on the top of Mount Hermon. AP

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.

Agence France-Presse