The Israeli army said on Wednesday it had "thwarted a terrorist cell" in Lebanon, accusing unidentified militants across the border of firing mortar shells at Israel while its war with Hamas raged.

The army said in a statement its forces had fired at the location in Lebanon from which "anti-tank missiles" were presumed to have been launched towards Israeli communities near the border.

Earlier on Wednesday, alerts were activated across northern Israel and the army said it had identified nine launches that crossed from Lebanese territory into Israel.

The military on Tuesday said it had killed at least four Lebanese fighters following attempted cross-border infiltration.

It did not say which, if any, groups the militants were affiliated with.

There are growing fears worldwide that Israel's war with Hamas could spread if the Iran-backed Hezbollah Islamist group in Lebanon were to intervene in northern Israel.

There have already been numerous clashes on the Lebanon-Israel border since Hamas launched a massive and bloody onslaught against Israeli communities and army bases near Gaza on October 7, killing more than 1,400, most of them civilians.

That triggered an unrelenting retaliation from Israel that has left at least 3,478 dead in the Gaza Strip, most of them ordinary Palestinians.

At least 20 people have been killed on the Lebanese side, including a Reuters journalist and two civilians, and at least three died in Israel.

The UN-patrolled border area between Lebanon and Israel — who technically remain at war — has remained largely peaceful since a devastating conflict in 2006 between Israel and Hezbollah.

"We are in a state of high alert… in the north," Israeli army spokesman Daniel Hagari said on Tuesday.

"If Hezbollah makes a grave error, we will respond with force."

Israel has began evacuating thousands of residents from some 28 communities near the boder in recent days, with the government authorising the army to order further evacuations — which for now it has not done.