A UN peacekeeping force in Lebanon Thursday confirmed that a tunnel discovered earlier this year by Israel had crossed the Lebanese-Israeli border, in the third such breach of a ceasefire resolution.

Israel in January accused the Iran-backed terrorist organization Hezbollah of having dug what it described as the deepest, “longest and most detailed” cross-border tunnel it had discovered.

The Israeli army said the tunnel from the Lebanese town of Ramyeh — just 800 meters (yards) from the border — reached a few dozen meters into Israel, and descended 55 meters (180 feet) underground.

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UNIFIL on Thursday said the tunnel was the third to have crossed the “Blue Line,” a demarcation line drawn by the UN to mark Israel’s withdrawal from southern Lebanon in 2000.

“UNIFIL’s independent assessment confirms that this tunnel crosses the Blue Line in violation of Resolution 1701” which ended the 2006 war between Israel and Hezbollah, it said.

“UNIFIL has informed the Lebanese authorities about the violation and has requested urgent follow-up actions,” the UN force said in a statement.

Lebanon and Israel are still technically at war. Israel is currently building a wall along the 130 kilometer (80 mile) frontier to block Hezbollah attempts to infiltrate.

In December, Israel accused Hezbollah of digging cross-border tunnels into its territory from southern Lebanon and launched an operation to destroy them.

According to the IDF, Hezbollah had planned to use the tunnels to kidnap or kill civilians or soldiers, and to seize a slice of Israeli territory in the event of any hostilities.

The IDF did not give a total figure for the tunnels found, though it announced in January that six were destroyed during the course of the operation. Five have been confirmed to exist by UNIFIL.

“Of these, three tunnels have been found to be crossing the Blue Line,” the peacekeeping force said on Thursday.

In recent years, Israel has carried out hundreds of airstrikes in Syria against targets linked to Iran, which alongside Hezbollah and Russia, are fighting on behalf of the regime of Syrian President Bashar Assad.

Israel has accused Iran of seeking to establish a military presence in Syria that could threaten Israeli security, and of attempting to transfer advanced weaponry to Hezbollah in Lebanon.

This once quiet fight has become increasingly public in recent months, with each side issuing public threats and warnings.

Last week, the commander of the IDF’s Ground Forces said Hezbollah was still planning to carry out a surprise invasion of northern Israel despite the recent anti-tunnel operation.

Maj. Gen. Yoel Strick told the Ynet news site the Iran-backed militia “still has plans to invade the Galilee.”

Strick, who was tapped to lead the Ground Forces in February amid criticism that Israeli troops were not prepared for war, said the IDF “of course won’t allow that to happen.”

Strick also voiced support for declaring war on Lebanon. “In the next war, it would be a mistake for us to distinguish between the state of Lebanon and Hezbollah, since Hezbollah is a political actor and part of the government,” he said.

In such a conflict, “if it were up to me, I would recommend declaring war on Lebanon and Hezbollah,” he said. “I have no doubt what the outcome will be… It will be a decisive victory.”

Hezbollah leader Hassan Nasrallah on Monday claimed Israel’s ground forces were unprepared for a military offensive in Lebanon.