Lebanon's Higher Defence Council gave orders on Wednesday to prevent Israel from building a border wall on Lebanese land, amid rising tensions over land and maritime boundaries.
Lebanese leaders have accused Israel of threatening the stability of the border region.
Arguments over the wall and Lebanon's plans to explore for offshore oil and gas in disputed waters have elevated tensions between them.
"This wall, if it is built, will be considered an assault on Lebanese land," the secretary general of Lebanon's Higher Defence Council said in a statement after meeting senior government and military officials.
"The Higher Defence Council has given its instructions to confront this aggression to prevent Israel from building (the wall) on Lebanese territory," it said, without elaborating.
Israeli officials did not immediately respond. Israel has previously said that the wall, and a disputed Mediterranean gas field, were on its territory.
Calm has largely prevailed along the frontier since 2006, when Israel fought a war with Lebanon's heavily-armed Shia Hezbollah movement.
The month-long conflict killed about 1,200 people in Lebanon, mostly civilians, and 160 Israelis, most of them troops. There has been no major confrontation between Israel and Iran-backed Hezbollah since.