BEIRUT (AP) — An explosion shook a Hezbollah stronghold in southern Lebanon on Tuesday, sending thick grey smoke billowing over the village, but the cause was not clear.

The blast occurred in the southern village of Ain Qana, above the port city of Sidon. There were no immediate reports of casualties.

An official with the Shiite militant group Hezbollah confirmed there was an explosion but declined to give further details. Another local Hezbollah official could not confirm or deny any casualties from the explosion and said the nature of the blast was not yet clear. Both spoke on condition of anonymity because they were not authorized to give official statements.

Members of the group imposed a security cordon, barring journalists from reaching the area.

Footage broadcast by the local Al Jadeed station showed damage to buildings.

The mysterious explosion comes seven weeks after the massive explosion at Beirut port, the result of nearly 3,000 tons of improperly stored ammonium nitrate detonating. The explosion killed nearly 200 people, injured 6,500 and damaged tens of thousands of buildings in the capital, Beirut.

It is still not clear what caused the initial fire that ignited the chemicals, and so far no one has been held accountable.