The Sirius Star owned by Saudi Aramco was bound for the U.S., and was seized on Sunday about 830 km southeast of Mombasa, Kenya. The hijacking was reported by the Navy on Monday and confirmed by the company.
The South Korean-made supertanker is carrying up to 2 million barrels of crude, equivalent to a quarter of Saudi Arabia's daily output.
The crew includes citizens of Croatia, Britain, the Philippines, Poland and Saudi Arabia, and is currently heading for the Somali port of Eyl.
Somali pirates have attacked around 83 ships so far this year, resulting in the seizure of around 33 vessels, including 200 crew members. The East African nation has been without a functioning government since 1991 and has no navy to police its coastline.
The Russian frigate Neustrashimy (Fearless) recently joined an international naval group that has surrounded a Ukrainian ship, the MV Faina, seized by Somali pirates on September 25. The Faina's Russian captain died of a heart attack after the vessel was seized.
The Russian frigate prevented on Sunday the seizure of the Rabikh vessel flying the Saudi flag by pirates off Somalia's coast.
