A big explosion rocked the southern Lebanese town of Tair Harfa on Monday, five km (three miles) from the border with Israel but there were no casualties, residents said.
A Lebanese security source said the blast was caused by a rocket that had been fired into Lebanon during the 2006 war with Israel but did not detonate on impact.
But Andrea Tenenti, a spokesman for the U.N. peacekeeping force in Lebanon, said UNIFIL soldiers in the area were still trying to ascertain the cause.
The explosion did kill several farm animals in a field, according to local residents.
A Reuters reporter said that members of the militant group Hezbollah, the Lebanese Army and around 50 members of UNIFIL were at the site of the blast but that he was prevented from approaching the area.
UNIFIL has about 12,000 troops and naval personnel in the country after its expansion under U.N. Security Council Resolution 1701 that halted the 2006 Israel-Hezbollah war in southern Lebanon. The south remains a Hezbollah stronghold.
Despite domestic demands for the group to disarm, Hezbollah keeps stockpiles of weapons - including thousands of rockets - saying it will need them in the event of a new war with Israel.
On October 3, three Hezbollah members were killed when an explosion ripped through a weapons warehouse in the eastern Lebanon town of Nabi Sheet.