A South Lebanon village, considered a stronghold of the outfit Hezbollah, was truck by a blast on Tuesday.
A resident said the blast at a house serving as "a Hezbollah centre" on the outskirts of Ain Qala had shaken the village.
Members of the Iranian-backed movement quickly cordoned off the area, an AFP photographer said.
Lebanon's NNA news agency said damage was limited to cracks in walls and broken glass, without reporting casualties.
A military source said preliminary information showed that "a Hezbollah centre containing munitions" was the source of the explosion.
The Lebanese army said it deployed a force to the site and had "initiated an investigation into the causes."
Footage shared on social media showed a huge plume of dark grey smoke rising from the site of the explosion.
Hezbollah did not immediately comment on the blast, but the source close to the group said the site was "not an arms depot".
Local media carried "unofficial" reports from Hezbollah members that the blast was caused by mines and other munitions dating back to the 2006 war between the group and Israel that an NGO had collected in order to destroy.
Hezbollah, backed by Iran, is the only Lebanese non-state armed group not to have disarmed after the country's 1975-1990 civil war.
It has fought several wars with neighbouring Israel, Iran´s arch-enemy.
NNA said the blast had coincided with intensive fly-overs by Israeli fighter jets and drones.
A spokesman for the Israeli army, which carries out regular overflights of its northern neighbour, declined to comment on the explosion.
Lebanon is still reeling from a massive explosion of hundreds of tonnes of ammonium nitrate at Beirut´s port last month that killed over 190 people, wounded thousands and ravaged swathes of the capital.
The blast led to the Lebanese government's resignation and a new cabinet line-up has yet to be agreed.