Under the truce that ended last year's war between Israel and Hezbollah, Lebanese troops have been deploying in the south and dismantling the Iran-backed militant group's infrastructure in the region.

The deaths come after the Lebanese government agreed this week to disarm Hezbollah and tasked the army with drawing up a plan to complete the process by year end.

Hezbollah has said it will ignore the cabinet's decision, which came under heavy US pressure, while its backer Iran said Saturday it opposed it.

An army statement gave a preliminary toll of six soldiers killed "while an army unit was inspecting a weapons depot and dismantling its contents in Wadi Zibqin", in Tyre district near the Israeli border.

Investigations were underway to determine the cause of the blast, it added.

A military source, requesting anonymity as they were not authorised to brief the media, told AFP the blast took place "inside a Hezbollah military facility".

Troops were "removing munitions and unexploded ordnance left over from the recent war" when the blast occurred, the source added.

President Joseph Aoun said he was informed by army commander Rodolphe Haykal of the "painful incident".

Prime Minister Nawaf Salam paid tribute to the troops who were killed "while performing their national duty", calling the army the protector of Lebanon's "unity and its legitimate institutions".

- 'Doing their job' -

The commander of the UN peacekeeping force in Lebanon (UNIFIL), Major General Diodato Abagnara, said the soldiers were "simply doing their job to restore stability and avoid a return to open conflict".

The blast came days after UNIFIL spokesman Andrea Tenenti said that troops had "discovered a vast network of fortified tunnels" in the same area.

UN spokesman Farhan Haq told reporters that the troops uncovered a cache of artillery, rockets, mines and improvised explosive devices.

In April, the Lebanese military said three soldiers were killed in a munitions blast, just days after another was killed in an explosion as troops dismantled mines in a tunnel.

Under the November ceasefire which sought to end more than a year of hostilities between Israel and Hezbollah, arms are to be restricted to Lebanese state institutions.

The government has tasked the army with presenting a plan by the end of August for disarming non-state actors.

- Ongoing strikes -

Lebanon's cabinet met on the issue twice this week, while Hezbollah has rejected the government's decision to take away its weapons.

A senior adviser to supreme leader Ayatollah Ali Khamenei said Saturday that Iran "is certainly opposed to the disarmament of Hezbollah".

"Iran has always supported the people and the resistance of Lebanon and continues to do so." international affairs adviser Ali Akbar Velayati told Iran's Tasnim news agency.

On Thursday, the government discussed a US proposal that includes a timetable for Hezbollah's disarmament, with Washington pressing Beirut to take action.

The government endorsed the introduction of the US text without discussing specific timelines, and called for the deployment of Lebanese troops in border areas.

It also called for the withdrawal of Israeli troops from five areas of the south they continue to occupy.

Israeli has kept up its strikes on Hezbollah targets in Lebanon despite the truce and has vowed to continue them until the militant group has been disarmed.

The Lebanese health ministry said one person was killed in an Israeli strike on Saturday on a vehicle in the town of Ainata near the border.