The soldiers "spotted three suspects, apparently Hezbollah activists, attempting to approach" an area where the army was carrying out engineering work in bad weather, the Israeli military said in a statement.

"Troops fired towards the suspects in accordance with the standard operating procedures. The three fled. The work in the area continues as usual."

A military spokeswoman told AFP the incident took place close to Yiftah, south of Metula, the town near which the tunnel from Lebanon was found.

Lebanon's official NNA news agency said Israeli forces fired shots in the air east of the village of Mays Al-Jabal after they had been surprised because of heavy fog by a routine Lebanese army patrol.

The Israeli army said on Tuesday it was launching an operation dubbed "Northern Shield" to destroy tunnels it said were dug across the border by the Shiite militant group Hezbollah.

The spokeswoman said on Saturday the works were connected to the operation.

On Thursday, UNIFIL, the UN body which monitors the border region, confirmed the existence of a tunnel in northern Israel originating on the Lebanese side of the border.

"UNIFIL is now engaged with the parties to pursue urgent follow-up action," it said.

Speaking with foreign diplomats in Israel on Thursday, Prime Minister Benjamin Netanyahu said he expected the UN's security council to convene on the tunnels.

"We think that Hezbollah should be condemned forcefully and universally on this act of aggression," Netanyahu said, as well as their backers Iran, and host country Lebanon.

"They're allowing their territory to be used in an act of aggression against a neighbouring state, and they allow their citizens to be used as pawns," he said of Lebanon.

Also Saturday, the Kremlin said Netanyahu called Russian President Vladimir Putin to tell him about the tunnel operation.

Putin "stressed the need to ensure stability along the line separating Israel and Lebanon," the Russian embassy in Israel said.

Iran-backed Hezbollah is the only group in Lebanon not to have disarmed after the country's 1975-1990 civil war.