There was an explosion on the perimeter fence of the compound of Italian oil company Agip, a unit of ENI, in Nigeria's oil city Port Harcourt on Monday, industry sources said, Reuters reported. The blast occurred within moments of a suspected car bomb attack on a Shell residential compound. There were no casualties in either explosion and no immediate impact on oil output from the world's eighth largest exporter. A militant group had earlier threatened to detonate three car bombs in strategic locations around the Niger Delta.