The Israeli military launched an operation on Tuesday to "expose and thwart" tunnels it says were built by the Hezbollah militant group that stretch from Lebanon into northern Israel.
The military said the tunnels were not currently being used by militants and that its work to find and neutralize them was taking place inside Israeli territory. However, the Israeli operation could send tensions soaring between Israel and its Iranian-backed foe, which have both been preoccupied with other conflicts since their last conflagration more than a decade ago.
"We see Hezbollah's activities as a flagrant and blatant violation of Israeli sovereignty" and of U.N. resolutions, said Lt. Col Jonathan Conricus, a military spokesman. "This activity is another example of the negative effects of Iranian entrenchment in the region."
The military did not disclose how many tunnels snake into Israeli territory from Lebanon nor what tools it was using to deal with the threat, although it said the operation could last for weeks. Israel has spent years attempting to tackle a network of tunnels from the Gaza Strip into Israel and has used a variety of methods to destroy tunnels and prevent them from being rebuilt.
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A Lebanese military official told The Associated Press that Lebanese troops and military intelligence agents, along with U.N. peacekeepers deployed in southern Lebanon, were observing the border on Tuesday. The official, who spoke on condition of anonymity in line with regulations, had no further details.
Israel has been using earthmovers and other large machinery to build a massive wall along its northern border, saying the barrier is needed to protect civilians from Hezbollah attacks. While the construction has prompted complaints from the Lebanese army, Hezbollah has not responded, an indication it could remain restrained amid the new operation.
Israel, meanwhile, gave no special orders to residents of northern Israel, signaling that it too was not expecting an immediate response from Hezbollah.
The existence of the tunnels did not appear to have surprised Israel.
Conricus said that Hezbollah has been developing an offensive plan against Israel that would "shift the battleground into Israel." The group would use firepower and ground units and "the surprise component of that plan was supposed to be tunnels that would allow infiltrators into Israel."
He added that Israel has investigated the possibility of underground Hezbollah tunnels since 2013 and that a task force has been searching for them for more than two years. He did not explain why the operation was launched now.
On Tuesday, bulldozers and military vehicles were seen operating near the pastoral Israeli border town of Metula. Residents of the area told Israeli media they had been hearing digging noises for years and had reported their suspicions to the military.
There was no immediate comment from Hezbollah and its Al-Manar TV did not make any mention of the Israeli operation.
An official from the so-called "Axis of Resistance" — a grouping led by Iran and made up of Syrian officials, Iraq Shiite militias, Hezbollah and other groups — said Hezbollah fighters were "on high alert to confront any possible Israeli aggression." The official spoke on condition of anonymity because he was not authorized to discuss the group's military activities with the media.
Malene Jensen, spokeswoman for the U.N. force in Lebanon known as UNIFIL, said the situation in the peacekeepers' "area of operation remains calm" and that they are in touch with all relevant parties to make sure calm and stability is maintained.
Israel and Hezbollah fought a month-long war in 2006 that ended in a stalemate. Israel's border with Lebanon has been relatively quiet in the years since, but Israel has continued to identify the Shiite militant group and its expanding weapons cache of tens of thousands of rockets as a major threat.
The Israeli operation began hours after Israeli Prime Minister Benjamin Netanyahu held a snap trip to Brussels to meet U.S. Secretary of State Mike Pompeo in which the two discussed "ways to halt together Iranian aggression in the region," including in Lebanon.
Israel has long voiced concern about Iran's growing military presence along its northern border, warning of an Iranian corridor that could assist in the transfer of weapons to Hezbollah. Israel has generally refrained from engaging in Syria's civil war, though it has carried out scores of airstrikes against what Israel says were Iranian shipments of advanced weapons bound for Hezbollah.
The operation comes weeks after Netanyahu faced a major crisis in his governing coalition over the handling of a cease-fire with Gaza militants. Amid the crisis he took on the defense portfolio from his resigning minister and promised to pursue a hard line against Israel's enemies during what he described as a "complex" security situation.
Although its attention has been diverted to violent protests along its border with Gaza in recent months, Israel's main security concerns lie to the north, along the border with Lebanon.
Israeli officials have long warned the threat posed by Gaza's Hamas rulers pales in comparison to that of Lebanon's Iran-backed Hezbollah — a heavily-armed mini-army with valuable combat experience and an arsenal of some 150,000 rockets that can reach nearly every part of Israel.
Hezbollah meanwhile has also been distracted by the war in Syria, where it has fought fiercely alongside Assad's troops. With Syria's civil war winding down, Hezbollah is now free to re-establish itself back home in Lebanon and refocus on Israel.
Neither side appears interested quite yet in another full-fledged confrontation like the 2006 war, but any skirmish could spark an all-out conflict along the tense border.
Associated Press writer Bassem Mroue contributed to this report.