A Japanese shipping company has hired a military attack specialist to investigate the cause of an explosion aboard an oil tanker that occurred in the Strait of Hormuz overnight Wednesday, Reuters reported.An official of shipper Mitsui O.S.K. said Thursday that initial reports that the explosion, which occurred aboard the tanker around 12:30 a.m., was caused by an earthquake-related wave are unlikely and a full investigation is being launched into the incident.Some of the ship's crew suffered injuries in the explosion. The tanker was returning to Japan with some 2.3 million barrels of oil collected from Qatar and Abu Dhabi. The ship was diverted to a UAE port after sustaining the damage. Port officials said there was no evidence of an attack but Japan's Transport Ministry has not ruled out the possibility.