An "external source" was responsible for an explosion that struck a Singapore-flagged oil tanker off the Saudi port city of Jeddah, the vessel's owner said on Monday. "BW Rhine has been hit from an external source whilst discharging at Jeddah... causing an explosion and subsequent fire onboard," Singapore-based shipping company Hafnia said in a statement, adding that there were no injuries in the incident. bur-ac/gle