The Israeli military says it has begun an operation to block what it calls “terror tunnels” dug into its territory by the Hezbollah movement in Lebanon.
It said it was neutralising the tunnels before they became operational and a threat to civilian communities.
It did not say how many tunnels there were, but said the operation would take place on Israel’s side of the border.
Tensions are high between Israel and Hezbollah, which fought a month-long war in 2006.
More than 1,125 Lebanese, most of them civilians, and some 40 Israeli civilians, were killed in that conflict.
It began when Hezbollah militants launched a raid into Israel, killing eight soldiers and kidnapping two others, who also died.
Israel has warned that another war with the group is likely and has said it will use massive military force in any new fight.
Hezbollah, which possesses one of the most powerful militias in the region, has threatened to attack Israel with its vast rocket arsenal if war breaks out.