Somali pirates are still in control of a supertanker hijacked with two Britons on board, the US Navy has said. The Saudi-owned television station Al Arabiya earlier said the Sirius Star had been freed, but the US Navy and Saudi Aramco, which owns the ship, both said they had no knowledge of any release. The Foreign Office confirmed two Britons were among the 25 crew members, along with people from Croatia, the Philippines, Poland and Saudi Arabia. The pirates seized the vessel 520 miles southeast of Mombasa, Kenya, capturing the biggest prize yet in a shipping zone where Somali raiders strike almost daily. The Sirius Star held a cargo of as much as two million barrels of oil - more than a quarter of daily Saudi Arabia's daily exports. Reports of the hijacking sparked rises in global crude oil prizes. She had been heading for the United States via the Cape of Good Hope at the southern tip of Africa, skirting the continent instead of heading through the Gulf of Aden and the Suez Canal. Lieutenant Nathan Christensen, a spokesman for the US Fifth Fleet, said: "This is unprecedented. It's the largest ship that we've seen pirated. It's three times the size of an aircraft carrier." There were no reports of damage to the ship, Mr Christensen said. He declined to say if the US Navy is considering taking action to rescue the tanker, saying: "We are evaluating the situation." He added: "The latest information we have is that they are taking the vessel to a Somali port. "We don't know the condition of the crew on board or the nature of the pirates' demands. In cases like this what we typically see is a demand for money from the ship owners but we haven't had that yet. "We don't know exactly where they are taking it but we know the town of Eyl is a pirate stronghold." Eyl is in the northern Puntland region of Somalia and has become notorious for pirate activity over the past months. Dozens of ships are thought to be being held captive there. Chaos in Somalia, where Islamist forces are fighting a Western-backed government, have spawned a wave of piracy. Shipowners have paid out millions of dollars in ransoms. Well over 60 vessels have been hijacked this year, driving up shipping insurance premiums and pushing some vessels to take longer routes between Asia and Europe than pass through the Suez Canal, increasing the cost of traded goods.