An oil tanker off Saudi Arabia’s port city of Jeddah suffered an explosion early Monday after being hit by “an external source,” a shipping company said, suggesting another vessel has come under attack off the kingdom amid its years-long war in Yemen. The Associated Press reports that the apparent attack on the Singapore-flagged BW Rhine, marks the fourth assault targeting Saudi energy infrastructure in a month. It also apparently shut down Jeddah port, the most-important shipping point for the kingdom. It also renews concerns about ship safety in the Red Sea, a crucial transit zone for global shipping and energy supplies that largely had avoided the chaos of regional tensions involving the U.S. and Iran last year.