Israel has been fighting Hezbollah since early March, sending troops into south Lebanon to battle the Iran-backed militant group after it launched rockets at Israeli territory, with the violence ongoing despite a shaky April 17 ceasefire.

Troops found "two Hezbollah terror tunnels, constructed over approximately a decade" that stretched for some two kilometres (1.2 miles) underground and were connected to firing positions directed at Israel, an army statement said.

Located in the Qantara area, troops used "over 450 tonnes of explosives" to demolish them, it said.

An Israeli military source described it as a "massive underground military installation" comprising an 800-metre tunnel and a second which ran for 1.2 kilometres, used as "an assembly area" for Hezbollah's elite Radwan forces.

He said it was "designed, sponsored and paid for by Iran" for the purpose of "raiding Israeli communities along the border".

Israeli Prime Minister Benjamin Netanyahu said the military would keep targeting Hezbollah's infrastructure.

"Today we blew up a huge Hezbollah terror tunnel. We are destroying their terror infrastructure, we are killing many dozens of their terrorists -- and we're not done yet," he said in a pre-recorded video.