Riyadh - A blast rocked a Singapore-flagged oil tanker at the Saudi port of Jeddah Monday, the vessel's owner said, with the kingdom saying it was struck by an explosives-laden boat in a "terrorist" assault. All 22 sailors aboard the tanker BW Rhine escaped unhurt after the blast struck just after midnight, Singapore-based shipping company Hafnia said, but it did not exclude the possibility of an oil spill. No group has so far claimed responsibility for what marks the latest in a string of attacks on Saudi energy sector targets, but it comes as Iran-backed Huthi rebels in neighbouring Yemen step up cross-border strikes against Saudi Arabia. "BW Rhine has been hit from an external source whilst discharging at Jeddah... causing an explosion and subsequent fire onboard," Hafnia said in a statement. "The crew have extinguished the fire with assistance from the shore fire brigade and tug boats," it added. The vessel was "attacked by an explosive-laden boat", the official Saudi Press Agency (SPA) reported, citing an energy ministry spokesman who condemned the "terrorist" attack. "The incident did not result in any casualties, and there was no damage caused to the unloading facilities, nor any effect on supplies," SPA said, without specifying who was behind the assault. "These acts of terrorism and vandalism, directed against vital installations, go beyond the kingdom and its vital facilities, to the security and stability of energy supplies to the world and the global economy." Jeddah, the second biggest Saudi city, is home to a key Red Sea port and distribution centre for oil giant Saudi Aramco. Hafnia reported "hull damage" in the blast. "It is possible that some oil has escaped from the vessel, but this has not been confirmed and instrumentation currently indicates that oil levels on board are at the same level as before the incident," it said. Dryad Global, a London-based maritime intelligence firm, also reported the explosion, saying it struck a vessel while "carrying out operations within the main tanker anchorage at the Saudi Aramco Jeddah port". The United Kingdom Maritime Trade Operations (UKMTO) said it was aware of an explosion and warned vessels in the area to exercise "extreme caution".