"The neutralisation and destruction phase of Hezbollah's attack tunnels dug from Lebanon into Israel has begun," the military said on its Twitter account.

"Our effort to expose additional tunnels continues according to plan," it added.

Since launching an operation to cut off the tunnels on December 4, the army says it has located four underground passageways infiltrating Israeli territory.

It issued a warning to Hezbollah, the Lebanese Shiite militant group with which Israel fought a devastating war in 2006.

"We have at our disposal infantry units, armoured units, stand-by aviation, naval units, all synchronised with clear orders and ready for a wide range of scenarios," said spokesman Lieutenant Colonel Jonathan Conricus.

The deployment was a "message to Hezbollah signifying that we will not tolerate any approach or attempt to interfere in our efforts to destroy these cross-border attack tunnels," he said.

Israel alleges Hezbollah had planned to use the tunnels to kidnap or kill its civilians or soldiers, and to seize a slice of Israeli territory in the event of any hostilities.

A month-long war in 2006 between Israel and Hezbollah killed more than 1,200 Lebanese, mostly civilians, and more than 160 Israelis, mostly soldiers.

Conricus said the operation to locate and destroy the tunnels was "purely defencive".

Their destruction would take several hours and would involve different techniques, he said, without giving further details.

The army advised Israeli authorities and UNIFIL, the United Nations peacekeeping mission in Lebanon, to notify its Lebanese counterpart to take measures to protect civilians across the border.

"We warn anyone not to approach the opening of the tunnels and not to stand near any of them on the Lebanese side," said the spokesman.