The explosion cause a fire in a garage which spread to flats
The Lebanese army and UN peacekeepers have begun investigations into Monday's blast at a Hezbollah member's house near the southern city of Tyre.
Hezbollah says that one person was wounded, while other reports said there had been one or more fatalities.
Reports are conflicting about the cause of the blast. Some sources said it happened when an Israeli shell left over from the 2006 war was dismantled.
Other reports say a Hezbollah rocket exploded by accident.
The blast reportedly destroyed a house north of Tyre in the village of Tayr Filsi, on the southern bank of Litani River.
Witnesses quoted by AFP news agency said the owner of the garage, Abdel Nasser Issa, had found a rocket on the river bank and had taken it to his garage where he dismantled it.
The 34-day conflict left the area littered with unspent ordnance dropped during the Israeli bombardment.
Israel said the blast "proved again the presence of weapons forbidden in southern Lebanon".
Hezbollah is banned from conducting military action south of the Litani, under the terms of the UN ceasefire following the 2006 war.