UN peacekeepers on Monday said that they confirmed the existence of four tunnels dug in areas "close" to northern Israel, as tensions flared between Israeli and Lebanese troops along the frontier.
It was not immediately clear if all the tunnels confirmed by Unifil were cross-border passageways, but the peacekeeping force had previously confirmed at least two cross-border tunnels beneath the border.
Meanwhile, a video circulated on social media showing Lebanese troops, accompanied by UN peacekeepers, asking Israeli soldiers to retreat to "behind the tree", after Israeli troops seemed to have crossed a border demarcation line to erect a barbed wire fence.
Lebanon's state-run news agency says Lebanese soldiers were on alert after Israeli troops unrolled barbed wire along the border.
The National News Agency said the incident on Monday occurred on the edge of the southern village of Mays Al Jabal when Israeli troops laid 200 metres of wire.
On December 4, the Israeli military announced an operation called "Northern Shield" to destroy tunnels it said had been dug by Hezbollah under the border.
The Lebanese group has not directly commented on the operation but its deputy leader, Naim Qassem, this month issued a warning that Hezbollah's rockets could strike "any point" inside Israel, including Tel Aviv.
In a statement on Monday, Unifil said the tunnels were of "serious concern," and noted that it has called on Lebanese authorities to ensure follow-up actions to resolve the issue.
On Monday Lebanese Prime Minister Saad Hariri and Lebanese Army Commander, Gen Joseph Aoun, met Unifil Commander, Gen Stefano Del Col, to discuss the situation.
According to the National News Agency, Mr Hariri assured Gen Del Col that Beirut is fully committed to the implementation of UN resolution 1701 and respected the Blue Line.
The Lebanese Armed Forces, he said, would conduct patrols and “deal with any flaw in the implementation of resolution 1701 from the Lebanese side”, but the UN “must shoulder its responsibilities in facing the daily violations by Israel of Lebanese airspace and territorial waters”.