Saudi-owned television station Al Arabiya said on Monday a Saudi crude tanker hijacked by Somali pirates had been freed, citing an unnamed official Saudi source.

The US Navy, which earlier reported the hijacking, said it had no information that the vessel had been released.

Saudi Aramco, which owns the supertanker, said it also had no knowledge of any release. 

Earlier, US Navy had said Pirates had taken control of the Saudi-owned oil supertanker Sirius Star.

It is the first oil tanker to have been seized by pirates in the area. The huge vessel can hold up to two million barrels of crude oil.

"We don't have any reports of any damage to the ship," said Lieutenant Nathan Christensen, a spokesman for the US Fifth Fleet. "We are evaluating the situation," he said when asked whether the navy was taking action to rescue the tanker.

He was unable to say how much crude was on the ship. The vessel has 25 crew from Croatia, Britain, the Philippines, Poland and Saudi Arabia, the US Navy said in a statement.

The tanker was attacked 450 nautical miles southeast of Mombasa, Kenya, it said.

Pirates, often based in anarchic Somalia, have made shipping routes off east Africa among the most dangerous in the world.

The Saudi vessel had been headed for the United States via the Cape of Good Hope at the southern tip of Africa. The route is a main thoroughfare for fully laden supertankers from the Gulf, the world's biggest oil exporting region.

The ship is Liberian-flagged, and owned and operated by state oil giant Saudi Aramco's shipping unit Vela International.