MOGADISHU : Somali pirates built up their defences around a captured Saudi Arabian super-tanker on Friday after demanding a 25 million dollar ransom.

As foreign navies sent warships to Somalia's dangerous waters and shipping companies sought alternative routes, extra clan militia and other fighters were brought in to strengthen security at the pirate lair of Harardhere, residents said.

"Some of them are inside the town and others are taking shelter in a nearby village and can be called if need be," local resident Mohamed Awale told AFP. He said the fighters had come from neighbouring Gulgudud and Mudug regions.

The Sirius Star, the biggest ship ever hijacked, and its 100 million dollar load of oil was seized last Saturday and taken to Harardhere, 300 kilometres (180 miles) north of lawless Somalia's capital Mogadishu.

The pirates on Thursday gave the owners 10 days to pay a 25 million dollar ransom.

Speaking in an exclusive interview from the tanker, a pirate who identified himself as Mohamed Said threatened "disastrous" consequences should Vela International, shipping arm of the Saudi oil giant Saudi Aramco, fail to comply.

"We are demanding 25 million dollars (20 million euros) from the Saudi owners of the tanker. We do not want long-term discussions to resolve the matter," Said told AFP.

"The Saudis have 10 days to comply, otherwise we will take action that could be disastrous," he said.

He did not specify the threatened action but the 330-metre (1,000 foot) long tanker is carrying two million barrels of crude oil, close to a quarter of Saudi Arabia's daily output.

Saudi Foreign Minister Prince Saud al-Faisal said Wednesday the owners were in talks with the pirates, but Vela International has remained tight-lipped.

Some experts have told AFP that the MV Faina, a Ukrainian ship seized by the same pirates in September with a cargo of tanks and other weaponry, was booby-trapped by the hijackers.

Environmental groups have warned of a huge catastrophe if oil from the super-tanker was released.

With close to 100 attacks on ships in the Gulf of Aden and Indian Ocean this year, the pirates now pose a growing threat to international trade.

Pirates with no confirmed links to bigger organsations and relatively modest means have seized ships of all sizes and in an ever-growing area.

Two speedboats with pirates armed with Kalashnikov rifles and rocket-launchers seized the Saudi tanker in 16 minutes on Saturday, according to a military report obtained by AFP.

The United States said it would seek support at the United Nations for a resolution to tighten international measures against Somali pirates.

The Indian frigate INS Tabar, one of dozens of warships from several countries protecting commercial shipping lanes in the Gulf of Aden, sank a Somali pirate ship Tuesday after coming under fire.

Russia announced it would send more warships to combat piracy and also called for an international ground military operation to crush piracy.

After the International Maritime Bureau (IMB) said the pirates were now "out of control," Arab nations bordering the Red Sea meting in Cairo on Thursday and pledged cooperation to end the threat -- but offered few specifics.

Oslo-based Frontline Ltd, the world's biggest oil tanker company, said that a more aggressive military approach was needed.

"I think that's the only solution," Martin Jensen, the company's acting chief executive officer told AFP.

Other maritime groups have decided to steer clear of Somalia's treacherous waters by diverting ships to the Cape of Good Hope, despite the extra delays and costs.

Giant Danish group A.P. Moller-Maersk has ordered some vessels to re-route.

"Vessels without adequate speed or freeboard will for the time being avoid the Gulf of Aden and seek alternative routing south of the Cape of Good Hope and east of Madagascar," the company said.

Somali Prime Minister Nur Hassan Hussein warned that piracy will rage unless the world helps restore a functional government in Somalia, which collapsed after the 1991 ouster of dictator Mohamed Siad Barre.

- AFP /ls