Tuesday, at least four people were killed and 20 others were injured in an explosion in Iraq’s southern city of Basra, sources told Reuters.

Police are still investigating the cause of the explosion, which occurred in the city center, near a main hospital.

The blas set fire to at least one vehicle and damaged a minibus.

Initial investigation showed that a motorcycle rigged with explosives could have been the cause of the blast, according to a police source.