"While a specialised army unit was carrying out an engineering survey of a site" in south Lebanon's Tyre district, "a suspicious object exploded, killing a member of the unit and moderately injuring three others", an army statement said.

A statement from Aoun's office said the soldiers had been "dismantling mines and explosive materials in a tunnel" in the area.

"Once again, the Lebanese army... is paying the price of extending state authority over the south and achieving stability there by implementing Resolution 1701," said Aoun, according to the statement.

United Nations Security Council Resolution 1701 ended a 2006 war between Israel and Hezbollah and formed the basis of a November truce that largely ended more than a year of fresh hostilities between Israel and the Iran-backed group.

The resolution called for the disarmament of all non-state armed groups, and said Lebanese troops and UN peacekeepers should be the only forces in south Lebanon.

Under the truce, Hezbollah was to withdraw its forces north of the Litani River, about 30 kilometres (20 miles) from the Israeli border, and dismantle any remaining military infrastructure in the south.

Israel was due to complete its pullout from Lebanon by February 18 after missing a January deadline, but it has kept troops in five places it deems "strategic".

During the war, Israel's army said it uncovered Hezbollah tunnels and tunnel shafts in south Lebanon.

A source close to Hezbollah told AFP on Saturday that the group had ceded to the Lebanese army around 190 of its 265 military positions identified south of the Litani.

Qatar-based network Al Jazeera quoted Aoun on Monday as saying that the army had dismantled tunnels and confiscated weapons without objection from Hezbollah, but had not yet deployed across the whole of the south.