The Israel Defense Forces on Tuesday launched an operation to destroy a number of cross-border attack tunnels that it says were dug by the Iran-backed Hezbollah group into northern Israel from Lebanon.

Announcing the launch of Operation Northern Shield, IDF spokesperson Lt. Col. Jonathan Conricus said “a number of tunnels” had penetrated Israeli territory and forces were working on the Israeli side of the frontier to destroy them.

“We see Hezbollah’s actions as a flagrant and blatant violation of Israeli sovereignty,” he said.

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The military said it believed these tunnels were for offensive purposes, unlike the tunnels and underground bunkers used by Hezbollah during the 2006 Second Lebanon War, which were primarily used for its defensive strategies.

Conricus said the tunnels “are not yet operationally ready” and therefore did not pose an “immediate threat.”

The operation came as tensions on Israel’s northern border have ramped up in recent days, and hours after Prime Minister Benjamin Netanyahu traveled to Brussels for a meeting with US Secretary of State Mike Pompeo to discuss Iran and security challenges on Israel’s northern border, likely referring to Hezbollah.

Israeli security chiefs were holding security assessments throughout the day on Tuesday in order to predict Hezbollah’s reaction to the IDF operation.

The Israeli military’s Arabic-language spokesperson called on Hezbollah members and Lebanese citizens to keep away from the tunnels. “You’ve been warned,” he wrote on Twitter.

Israel has long said that Hezbollah planned to conduct cross-border raids in any future conflict, with the specific goal of attacking and conquering a civilian town near the border. Northern residents have raised fears in recent years of attack tunnels being dug under the border, spurring the IDF to launch a task force to investigate the concerns in 2014.

“[Hezbollah’s] main goal is to kill as many people as they can in [Israeli] villages and army bases,” a senior officer IDF officer said earlier this year, in a briefing to reporters on the Lebanese border.

The IDF operation began in the predawn hours of Tuesday morning. The military declared the area around the community of Metulla a closed military zone, but gave no other special instructions to Israeli civilians in the area.

The army said the operation was expected to expand to other locations along the Israeli-Lebanese border in the coming days. A spokesman said the operation might last weeks.

Additional troops were deployed to northern Israel as a precaution against potential attacks by Hezbollah, but no reservists were called up.

Conricus would not comment on whether additional air defenses were deployed to the area as a precautionary measure as well, but military sources said the IAF and IDF special forces were braced for any eventuality. Hezbollah is believed to have an arsenal of over 100,000 rockets and missiles.

Last Friday, the Lebanese terror group issued a warning video to Israel apparently filled with satellite images and precise map locations of strategic sites in the Jewish state, with a message: “Attack and you will regret it.”

The video was posted after an alleged Israeli airstrike on Iranian and Hezbollah targets in Syria the night before.

The video, with Hebrew subtitles, opened with scenes of Hezbollah fighters preparing to launch rockets and leader Hassan Nasrallah warning that the Lebanese terror group would respond to any attack on Lebanon.

Attack tunnels were long rumored to have been dug from southern Lebanon into Israeli territory by the Iran-backed terror group, but in recent years Israeli defense officials repeatedly either denied their existence or refused to discuss the matter.

The IDF spokesperson accused Iran of providing the funding and support for Hezbollah’s tunnel program.

“We’ll be dealing with that in the next few days too,” the army said.

According to the Israeli military, the Gaza-ruling Hamas terror group also provided Hezbollah with technical assistance, based on its extensive experience digging attack tunnels from the Strip into southern Israel.

Conricus also accused the Lebanese government of failing to prevent Hezbollah from establishing a military presence in southern Lebanon, despite this being a violation of United Nations Resolution 1701, which ended the 2006 Second Lebanon War and called for all armed groups besides the Lebanese military to remain north of the country’s Litani River.

A spokesperson for the UN peacekeeping force UNIFIL, which is meant to enforce UN Resolution 1701, told The Times of Israel that it was aware of the reports that the IDF was launching Operation Northern Shield and was maintaining contact with “all relevant interlocutors to ensure that the parties use the UNIFIL liaison and coordination mechanisms to maintain the continued calm and stability.”

“The situation in UNIFIL’s area of operation remains calm,” the UNIFIL spokesperson said.

Conricus said he could not elaborate on the number of tunnels or how deeply they penetrated into Israel, but said such information may be provided in the future.

The IDF spokesperson would not comment on how the military sought to destroy the alleged Hezbollah tunnels, but said it would use some of the techniques and technologies it employs in countering the attack tunnels dug into Israel from the Gaza Strip.

“It will take time to neutralize and expose all the tunnels,” the IDF spokesperson said.

The spokesperson said units from the IDF Northern Command, Military Intelligence, Combat Engineering Corps and Ministry of Defense will lead Operation Northern Shield.

The project to find these alleged Hezbollah tunnels began in 2013 when residents of northern Israel reported hearing the sounds of underground construction, but the initial checks turned up no evidence of tunnels.

“Every complaint was checked with the technologies and capabilities available at that time. We could not substantiate those complaints,” IDF Spokesperson Brig. Gen. Ronen Manelis told the Kan broadcaster on Tuesday morning.

In October 2014, following the Gaza war earlier that summer in which Hamas attack tunnels played a key role, the IDF established a new task force, made up of intelligence and technology units, with the aim of “detecting and exposing Hezbollah’s offensive tunnel program,” the IDF spokesperson said.

In recent years, the Israeli military and Defense Ministry have been bolstering defenses along the Israeli-Lebanese border: setting up berms, clearing vegetation, creating artificial cliffs and building nine-meter-tall concrete walls.

The barriers are designed to serve two main functions: protect Israeli civilians and soldiers from sniper attacks, and prevent infiltration into Israel by Hezbollah operatives.

According to the IDF senior officer, approximately seven years ago, Hezbollah created a special forces unit — known as the Radwan Unit — specifically tasked with crossing into Israel and causing as much mayhem and destruction as possible both for the sake of the destruction itself and for the “symbolism” of having troops carry out attacks inside Israel.

Israel fought a punishing war with Hezbollah in 2006, which has since given way to relative quiet along the frontier. However, Israeli officials have raised alarms over Iran arming Hezbollah, via Syria or directly into Lebanon, with precision missile technology.

On Monday, Netanyahu was reportedly slated to request that Pompeo pass a message to Beirut that Israel would act militarily if it did not crack down on Hezbollah.

Times of Israel staff contributed to this report.