"The supertanker will anchor off Garaad," said Abdi Yare, a pirate chief based in Hobyo, another pirate lair 200 kilometres (120 miles) further south.

Garaad is a fishing village 750 kilometres (450 miles) north east of the capital Mogadishu. It lies on the border of the self-proclaimed autonomous region of Puntland and central Somalia.

Mohamed Said, a pirate in Garaad confirmed to AFP that some of his colleagues from the coastal village were among those who hijacked the vessel.      "The group is headed by a big pirate chief. They used four speedboats and a mother ship for the attack," he said.

The Irene SL was seized by pirates off the coast of Oman as it was heading for the US with 270,000 tonnes, or 1.9 million barrels of crude oil from Kuwait on board.

"It's a good catch and there must be about 30 pirates on board," Abdi Yare told AFP.

Several small boats have left Hobyo to escort the supertanker in towards shore, other pirates in Hobyo said.

Twenty-five crew members were on board at the time of the attack: seven Greeks, one Georgian and 17 Filipinos.

On Tuesday an Italian tanker with a capacity of 105,000 tonnes and with 22 crew members on board was also captured by pirates in the Indian Ocean.