hezbollah tunnels lebanon israel
© Associated Press/Mohammed Zaatari
An Israeli military digger works on the Lebanese-Israeli border next to a wall that was built by Israel in the southern village of Kafr Kila, Lebanon, Tuesday, Dec. 4, 2018.
The United Nations Interim Force in Lebanon (UNIFIL) has confirmed the existence of all four of the tunnels that the Israeli Defense Forces (IDF) discovered along the border between Israel and Lebanon, UN Spokesman Stephane Dujarric said in a press briefing on Monday.

"Based on the UN's independent assessment, the peacekeepers have so far confirmed the existence of all four tunnels close to the Blue Line in Northern Israel," Dujarric said, referring to the UN-drawn line of demarcation between Israel and Lebanon. "UNIFIL at this stage can confirm that two of the tunnels cross the Blue Line."

The UN spokesman emphasized that the presence of cross-border tunnels is "a matter of serious concern," adding that UNIFIL has demanded that the Lebanese government respond to the violation of UN Security Council Resolution 1701, which calls on both sides to respect the Blue Line and implement a full cessation of hostilities.

The spokesman's comments come after last week, the IDF discovered a fourth cross-border tunnel that it says the Hezbollah militant group dug into Israel from southern Lebanon.

In late November, the Israeli army launched an operation, dubbed Northern Shield, to expose and neutralize cross-border attack tunnels that Hezbollah dug from Lebanon into Israel.

Israel views Hezbollah's presence in Lebanon and Syria as a threat to its national security and accuses Iran, its main rival in the region, of backing it.