DUBAI, United Arab Emirates (AP) — The chief official at the port where a Japanese tanker was docked a day after it was damaged at the mouth of the Persian Gulf said Thursday investigators now believe the ship was involved in a collision, backing away from an earlier theory that natural causes were to blame.

But the ship's owner refused to speculate on what had set off Wednesday's incident, which it described as an explosion on the tanker, until it had more information. The company initially said it suspected the ship had been attacked as it entered the tense Strait of Hormuz. The possibility of a deliberate attack has not been ruled out.

Captain Musa Murad, director general of the port of Fujairah, said damage to the ship's hull and interior is being investigated, but that clues point to a crash of some sort. The ship dropped anchor at the Emirati port for inspections late Wednesday.