The bitumen tanker MV Asphalt Princess is heading into the congested approach to the Strait of Hormuz, it said.
It is not clear who has seized the ship but analysts says Iranian forces will be suspected.
Iran's Revolutionary Guards dismissed the reports as a pretext for "hostile action" against Tehran.
The incident comes less than a week after an oil tanker operated by an Israeli-owned company was attacked by a drone off Oman, killing two security guards - one British and the other Romanian.
