The United States denied an Israeli request to place sanctions on Lebanon, a day before the IDF launched an operation to uncover and destroy what it says is a network of cross-border tunnels snaking into the country from its northern neighbor, a senior Israeli official has reportedly said.

Meeting with Prime Minister Benjamin Netnayahu in Brussels last Monday, US Secretary of State Mike Pompeo rejected the premier’s proposal to slap Beirut with a an economic embargo for its ostensible support for Hezbollah, Haaretz quoted a senior Israeli official as saying on Wednesday.

Pompeo reportedly cited the US’s strategic ties with Lebanon.

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Instead, the secretary of state agreed to increase measures against the Iranian-backed Hezbollah terrorist group, which Israel says planned to used the tunnels as a surprise component of an opening salvo in a future war, to allow dozens or hundreds of terrorists into Israel, alongside a mass infiltration of operatives above-ground and the launching of rockets, missiles, and mortar shells at northern Israel.

Pompeo told Netanyahu during the meeting that the US was committed to “confronting the totality of the Iranian regime’s threats through maximum pressure,” according to a State Department statement released at the time.

In a public statement before the closed-door talks, Netanyahu thanked Pompeo for the administration’s “strong” stance on Iran, and said he looked forward to discussing joint Israeli-US efforts to “curb Iran’s aggression in the region, in Syria, in Iraq, in Lebanon and elsewhere.”

Netanyahu told Pompeo that sanctions were justified against Lebanon as it was responsible for Hezbollah’s violation of UN Resolution 1701 which set the terms for the end of the 2006 war between Israel and the terror group, the official was reported as saying.

On Tuesday, the US House of Representatives approved a bill that would target for sanctions Hezbollah and the Gaza-based Hamas terror group for using civilians as human shields, guaranteeing that it will become law.

“This critical and timely legislation mandates new sanctions against Hamas, Hezbollah and foreign state agencies that use civilians as human shields or provide support to those doing so,” the American Israel Public Affairs Committee said in a statement after the House passed the bill. The Senate passed the measure in October.

The bill calls Hezbollah and Hamas “repeated” practitioners of an action that violates international law. It notes reports that Hezbollah is concealing missiles in villages in Lebanon and that Hamas routinely launches missiles at Israel from densely populated areas.

The bill, which had bipartisan backing, now goes to US President Donald Trump for his signature.

Amid the ongoing tunnel operation, Netanyahu on Tuesday warned Hezbollah that it would face an “unimaginable” response if it tried to interfere with IDF efforts.

Netanyahu made the threat while touring the northern border, where troops have been working since last week to find the attack tunnels and render them unusable.

“If Hezbollah makes the mistake, and decides, in any way, to attack us or to oppose our operation, they will be hit with unimaginable blows,” Netanyahu vowed, as the army said it uncovered a third Hezbollah cross-border attack tunnel that penetrated Israeli territory from southern Lebanon.

The army said it had drilled into the passage and planted explosives inside it to ensure it cannot be used.

Netanyahu said the army had secretly tracked the tunnel-digging project before launching Operation Northern Shield, deflecting criticism that the military had allowed the terror group to build up attack infrastructure under the border.

“They thought they were undetected, but we knew and we planned,” Netanyahu said. “We kept it secret and it did not leak. We have planned this with great attention to detail and we are carrying out exactly what we planned.”

The army has also said it is aware of the existence of other tunnels, but has yet to fully expose them.

The operation has raised tensions of a possible fresh conflict on the volatile border, which has seen two wars in recent decades, though Lebanon has downplayed chances of war so long as Israeli troops do not cross the border. UN peacekeepers have also stepped up patrols to ensure the frontier remains calm.

Netanyahu said Israel was “completely prepared” for any challenges.

JTA contributed to this report.