An Israeli crane is seen by a wall built near the border with Lebanon, Nov. 27, 2018. Photo: Reuters / Ali Hashisho.

Israel said on Tuesday it had launched an operation to “expose and thwart” cross-border attack tunnels from Lebanon dug by the Iran-backed Lebanese movement Hezbollah.

The army said the operation was for now confined to Israel and did not extend into Lebanon, where the tunnels originated. The broader frontier appeared calm in the hours after the announcement, despite fear that it could lead to confrontation.

There was no immediate comment from Hezbollah. A Lebanese army source said the situation was calm on its side of the border, as did UN peacekeepers operating there.

Israel released video footage of digging and pile-driving equipment at work in unidentified locations, carrying out what it said were “tactical preparations to expose Hezbollah’s offensive cross-border tunnel project.”

It later published a photograph of a tunnel that it said it had uncovered. Israel said the tunnel originated under a house around the Lebanese village of Kfar Kela and crossed the border near Israel‘s northernmost town, Metula.

Reuters could not immediately verify the photo or the footage.

Israel and Hezbollah have avoided any major conflict across the Lebanese-Israeli border since their last war in 2006, though Israel has mounted attacks in Syria targeting what it said were advanced weapon deliveries to the Shi’ite Muslim group.

On Monday, Israeli Prime Minister Benjamin Netanyahu met US Secretary of State Mike Pompeo in Brussels to update him on the imminent tunnel operation.

“Whoever tries to harm Israel will pay a heavy price,” Netanyahu said in a statement after returning to Israel early in the morning.

Hints, threats

The military said the tunnels were not yet operational but posed “an imminent threat” to Israeli civilians, and constituted “a flagrant and severe violation of Israeli sovereignty.”

It said the army had boosted its presence and readiness and was prepared for “various scenarios”.

The operation could take weeks, an Israeli military source said.

Its Arabic media spokesman posted a message on Twitter warning the Lebanese army and Hezbollah to stay away, saying: “Your lives are in danger, you have been warned.”

In September, Netanyahu identified three locations in Lebanon where, he said, Hezbollah was converting “inaccurate projectiles” into precision-guided missiles. Last month he also hinted at an upcoming Israeli offensive during a televised address, but did not give details.

Last year, Hezbollah’s leader said any future conflict with Israel could take place inside Israeli territory, and there would be “no place that is out of reach of the rockets of the resistance or the boots of the resistance fighters”.

Israel‘s vulnerability to tunnels was laid bare during its war with Hamas in the Gaza Strip in 2014 when Palestinian fighters used dozens of secret passages dug from Gaza into Israel to launch surprise attacks.