Lebanon's southern border has seen near daily exchanges of fire, mainly between Israel and Hamas ally Hezbollah, since Hamas launched a shock attack on Israel from the Palestinian territory on October 7.
"Lebanon doesn't need a war, that's the least we can say," Lecornu said during a visit to French peacekeepers in the United Nations Interim Force in Lebanon (UNIFIL).
Such a war "could have major escalatory effects on the whole region," he added.
The cross-border exchanges have left 66 dead on the Lebanese side -- 48 of them Hezbollah fighters but also including seven civilians, one of them a Reuters journalist, according to an AFP tally.
On the Israeli side, nine people have died -- eight soldiers and one civilian, the army says.
On Saturday, a UN peacekeeper was wounded by shelling, the mission's spokesman said, hours after reporting a hit on its headquarters.
Iran-backed Shiite militant group Hezbollah has been targeting Israeli observation posts and military positions near the border.
The group's leader Hassan Nasrallah is to speak on Friday for the first time since the Israel-Hamas war broke out.
Lecornu said there was no interest in interrupting UNIFIL's mandate in the face of the current border tensions, adding he had heard "here and there that UNIFIL should stop its patrols".
"If there was ever a time in which we needed oversight and deterrence to prevent an escalation, it's now," he said.
UNIFIL acts as a buffer between Lebanon and Israel, which remain technically at war, and counts around 10,000 peacekeepers, some 700 of them French.
Israel says its aim in Gaza is to destroy Hamas following the October 7 attacks, the deadliest in the country's history, in which officials say militants killed 1,400 people and kidnapped 242 others.
It has bombed Hamas-ruled Gaza relentlessly since then, a bombardment the Hamas-run health ministry says has killed more than 9,000 people.
