Under a November truce deal that ended a war between Israel and Iran-backed Hezbollah, the army has been deploying in south Lebanon and dismantling the militant group's infrastructure there.

"An army officer and two soldiers were killed and a number of citizens were injured due to an explosion of ammunition as it was being transported inside an army vehicle" in Braiqaa, in south Lebanon's Nabatiyeh district, an army statement said.

Specialised army units were investigating the circumstances of the incident, the statement added.

An AFP correspondent in Braiqaa, around 20 kilometres (12 miles) from the Israeli border, saw several charred and burnt vehicles on the road, with some damage to nearby shops and flats.

The army had cordoned off the area.

President Joseph Aoun offered his condolences for the three servicemen "who fell while performing their mission to preserve security and stability" and to keep south Lebanon residents from harm, a presidency statement said.

On Monday, the army said a soldier was killed and three others wounded in an explosion in the country's south, where Aoun said they had been dismantling mines in a tunnel.

According to the ceasefire, Hezbollah was to pull its fighters north of Lebanon's Litani River. Israel was to withdraw all its forces but has kept troops in five places it deems "strategic".