JERUSALEM — Israel started a military operation on Tuesday to expose and thwart offensive tunnels Hezbollah had been building across the Lebanese border, the military said, the first time that Israel has taken open action to combat underground passageways in the already volatile north.
The effort, called Operation Northern Shield, was aimed at an unspecified number of tunnels in the area of Metula, said Lt. Col. Jonathan Conricus, a spokesman for the Israel Defense Forces.
None of the tunnels were ready to be used, he said, and the army was neither asking civilians in the area to evacuate nor calling up reserves. But it declared an area around Metula, in the northernmost reaches of the Galilee panhandle, a closed military zone and said it had “enhanced its presence and readiness” in the north and was “prepared for various scenarios.”
Prime Minister Benjamin Netanyahu said the early stages of the operation had already proven successful.
“Whoever tries to harm the state of Israel will pay a heavy price,” he said in a statement. He added that Israel would continue to act, “openly and covertly, to ensure the security of Israel.”
Brig. Gen. Ronen Manelis, the chief military spokesman, said Israel was prepared for a “broad operation over several weeks.” It was expected to extend beyond the Metula area, along the border.
The military also warned Hezbollah and soldiers of the Lebanese Army to stay away from the tunnels, saying their lives were in danger, though Israeli officials emphasized that for now the operation was taking place on the Israeli side of the border.
The military operation comes as Mr. Netanyahu faces growing legal troubles. On Sunday, the Israeli police recommended that he be indicted on bribery, fraud and other charges in a case involving accusations he traded regulatory favors for fawning news coverage — the third, and potentially the most damaging, in a series of corruption cases against him this year.
Some critics of Mr. Netanyahu immediately began speculating whether the operation had been timed as a distraction from his legal woes and to burnish his image as Israel’s security czar.
But the army and some security experts quickly worked to dispel the notion that the timing was politically motivated. Colonel Conricus said the army’s general staff had been preparing the operation for more than a year and a half. The timing, he said, had to do with the fact that the tunnels had crossed the border but were not yet fully operational. The idea, he said, was “to nip them in the bud” before they posed an immediate threat to Israeli civilians.
With the winding down of the civil war in neighboring Syria, Israel appears to have increasingly shifted its focus to Lebanon. Hezbollah, the Lebanese Shiite organization backed by Iran, has been fighting for years against insurgent groups in Syria to defend the rule of President Bashar al-Assad, and Israel has been working intensively to prevent Iran’s efforts to entrench itself in Syria.
But Israel has also been warning in recent months of Iranian efforts to strengthen Hezbollah in Lebanon, making a future conflagration seem inevitable.
While Israeli experts said the action against the tunnels could lead to an escalation, it was not immediately clear if, or how, Hezbollah would respond.
“Now the ball is in the Hezbollah court,” said Yaakov Amidror, a former Israeli national security adviser and retired general. “They can react and the reaction to their reaction might be devastating,” he told reporters on Tuesday, in an apparent effort to deter Hezbollah.
Mr. Amidror said the operation was occurring now because the technological, operational and intelligence efforts were complete and Israel had worked to lay the diplomatic groundwork.
There appeared to be no immediate response to the Israeli operation on the Lebanese side of the border. The state-run National News agency said the border area was calm and that United Nations monitors were running patrols in the area to keep watch on the situation.
There was no official comment from Hezbollah. But last year, its leader, Hassan Nasrallah suggested that Hezbollah fighters would try to infiltrate Israel in a future conflict, staying that there would be “no place that is out of reach of the rockets of the resistance or the boots of the resistance fighters.”
Israel has been building defensive obstacles along a roughly seven-mile stretch of its border with Lebanon since 2015, constructing fences, clearing vegetation and creating steep cliffs to deter invading forces. Those efforts are aimed at thwarting what Colonel Conricus said was Hezbollah’s goal of assuring that the next battlefield between Israel and Lebanon would be inside Israeli territory.
The operation came a day after Mr. Netanyahu met in Brussels with Secretary of State Mike Pompeo to discuss curbing Iranian aggression in the region. Mr. Netanyahu said he had updated Mr. Pompeo about the impending tunnel-clearing operation.
Israeli officials have accused Iran of helping Hezbollah build underground factories in Lebanon to upgrade the militant group’s arsenal of missiles, which experts said posed an even greater threat than the tunnels. In addition, Israeli news outlets have reported that Iran has been flying advanced weaponry directly to Beirut, bypassing overland routes through Syria that Israel has repeatedly bombed.
But Israel kept its plans for the tunnel operation, and even its knowledge of the existence of such cross-border tunnels, completely under wraps, taking Hezbollah and the Israeli public by surprise with Tuesday’s action.
The military said it had been gathering intelligence and developing operational and technological abilities to deal with the northern tunnels since 2014. Israel has been steadily detecting and destroying cross-border attack tunnels from the Palestinian territory of Gaza, in the south, for years.
Israel said the Hezbollah tunnels constituted “a flagrant and severe violation of Israeli sovereignty” and violated U.N. Security Council Resolution 1701, which formalized the cease-fire that ended a devastating, monthlong war between Israel and Hezbollah in the summer of 2006.
Mr. Netanyahu had hinted recently that Israel would soon embark on a military campaign of some sort, warning darkly that it would “require sacrifice.” The warning came in mid-November, when Mr. Netanyahu delivered a live, televised speech in which he urged his teetering coalition partners not to topple the government at what he called a complex time for national security. To do so, he said, would be “irresponsible.”
The political crisis was precipitated by the resignation of the hard-line defense minister, Avigdor Lieberman, who cited the government’s lack of resolve in handling the latest conflict with Gaza, a botched spy mission by Israel that led to exchanges of rocket fire. Israel agreed to a cease-fire that brought a hasty, if inconclusive, end to that round of fighting in the south.
Mr. Netanyahu said at the time that Israel was “in the midst of battle,” and that he had “a clear plan.” He also announced that he was taking on the role of defense minister.
Hours into the military operation, the army announced it had exposed and was preparing to neutralize a tunnel running about 130 feet into Israeli territory from under a house in the Lebanese village of Kela.
Israel has long tried to draw international attention to what it says are Hezbollah’s efforts to build up its firepower in southern Lebanon, pointing to arms depots, rocket-launching sites and signs of tunnels in Shiite villages close to the border.
But Israel has never before revealed its knowledge of Hezbollah tunnels running into its territory, despite the complaints of Israelis living close to the northern border about strange sounds coming from underground, as if the Lebanese militants were digging beneath their homes. In the wake of the complaints the military began a drilling operation in early 2015. It denied finding anything in those specific areas at the time.