Israel's vulnerability to tunnels was laid bare during its war against Hamas in Gaza in July and August. What began as shelling exchanges with Hamas escalated into a ground offensive after Palestinian militants used dozens of secret passages dug from Gaza into Israel to launch surprise attacks.
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Residents of northern Israel, who were battered by Hezbollah rockets during the Second Lebanon War in 2006, have at times reported underground noises suggesting that guerrillas were burrowing across the frontier in a new tactic.
The IDF says searches it has carried out have turned up nothing.
"We have no positive information meaning that there are tunnels. The situation is not similar to what there was around the Gaza Strip," Major-General Yair Golan, commander of Israeli forces on the Lebanese and Syrian fronts, told Army Radio.
"That said, this idea of going below ground is not foreign to Lebanon and is not foreign to Hezbollah and so we have to suppose as a working assumption that there are tunnels. These have to be looked for and prepared for."
Hezbollah does not comment on its military capabilities. Spurred by the Gaza experience, the Israelis say they hope to develop effective tunnel-hunting technologies within two years.
Golan said Hezbollah, which is fighting on the side of President Bashar Assad in the civil war in Syria, appeared unlikely to seek a renewed conflict with Israel.
Were that to happen, he said, Israel would hit Lebanese targets hard but would also suffer from a Hezbollah rocket arsenal believed to be 10 times more potent than Hamas's.
There have been occasional attacks along the border in recent weeks, however, including a roadside bomb planted by Hezbollah that wounded an Israeli soldier. Israel responded by firing artillery shells into southern Lebanon.
"We will not be able to provide the umbrella that was provided in the south by Iron Dome," Golan said, referring to an aerial interceptor system which Israeli and US officials say scored a 90 percent shoot-down rate against Gazan rockets.
"We and Hezbollah are conducting a kind of mutual-deterrence balance," he said, while cautioning that isolated flare-ups on the border could still boil over into war.
"There is no absolute deterrence. Each side has its pain threshold, its restraint threshold, which when passed prompt it to take action."