The Lebanese army and UN peacekeepers have begun investigations into an explosion at a Hezbollah member's house near the southern city of Tyre.
Hezbollah said one person had been wounded on Tuesday, but some news agencies reported up to five people may have died when old ordnance stored in a garage exploded.
Initial reports suggest a rocket exploded - a shell left over from Israel's last invasion of southern Lebanon in 2006.
Other reports say a Hezbollah rocket exploded by accident.
The explosion destroyed a house about 20km north of Tyre in the village of Tayr Filsi, on the southern bank of the Litani river.
Villagers told the AFP news agency that the owner of the garage, Abd al-Nasir Isa, had found a rocket on the river bank and had taken it home to dismantle it.
The 34-day conflict in 2006 left the area littered with unspent ordnance dropped during the Israeli bombardment.
However, Israel said the blast proved that weapons forbidden in southern Lebanon were being stored by Hezbollah, which is banned from conducting military action south of the Litani under the terms of the UN ceasefire.