Hezbollah warns Israel against Lebanon border flare-up
Naim Qassem, number two in the Iran-backed Lebanese group, was speaking after Defence Minister Yoav Gallant said Israel was determined to restore security to its northern front.
Gallant told Israeli troops last week that "we are preparing for anything that may happen in the north".
In a speech in Beirut, Qassem said: "We have no intention of going to war, as we consider that this would not be useful.
"However, if Israel does unleash a war, we will face up to it -- and there will be large losses on both sides," he said.
"If they think such a war would allow the 100,000 displaced people to return home ... we issue this warning: prepare to deal with hundreds of thousands more displaced."
Hezbollah has traded near-daily fire with Israeli forces in support of ally Hamas since the Palestinian militant group's October 7 attack on Israel triggered war in Gaza.
Thousands of people living in the border area of both countries have been displaced by the fighting.
The cross-border violence since early October has killed 623 people in Lebanon, mostly fighters but also including at least 142 civilians, according to an AFP tally.
On the Israeli side, including in the annexed Golan Heights, authorities have announced the deaths of at least 24 soldiers and 26 civilians.
Qassem said on Saturday of those displaced in Israel: "It is impossible to bring them back, no matter the sacrifices made.
"So take your time and think about it before reaching a decision. We are prepared for any eventuality."
In late August, Israel's military said it had foiled a major assault by Hezbollah aimed at avenging a military commander killed by an Israeli air strike near Beirut.
Israel said it destroyed "thousands" of Hezbollah rocket launchers, while the Lebanese group insisted it had fired a drone and rocket barrage across the border.
It was perhaps the biggest exchange of fire between Israel and Hezbollah since the Gaza war began.
However, the violence has since eased, with analysts believing that both sides wish to avoid a wider regional flare-up.