The buccaneers have taken a Thai fishing boat, a Greek bulk carrier and a Hong Kong-flagged ship heading to Iran since Saturday's spectacular capture of a Saudi supertanker carrying US$100 million (S$152 million) of oil, the biggest ship hijacked in history.

Saudi Arabia said the supertanker's owners were in talks over a possible ransom, despite official reservations about negotiations with hijackers. Iran said it was seeking contact with the Hong Kong ship it had chartered to import grain.

The explosion of piracy off Somalia this year has driven up insurance costs, made some shipping companies divert around South Africa and prompted an unprecedented military response from NATO, the European Union and others.

'The pirates are sending out a message to the world that 'we can do what we want, we can think the unthinkable, do the unexpected',' Andrew Mwangura, coordinator of the East African Seafarers' Assistance Programme, told Reuters in Mombasa.

India's navy said one of its warships destroyed a pirate ship in the Gulf of Aden in a brief battle late on Tuesday.

'Fire broke out on the vessel and explosions were heard, possibly due to exploding ammunition that was stored on the vessel,' the navy said, adding that two speed boats sped away.

The International Maritime Bureau said pirates from the Horn of Africa nation had hijacked a Thai fishing boat with 16 crew.

That followed the capture of the Hong Kong-flagged ship carrying grain bound for Iran.

Mwangura's group said a Greek bulk carrier had also been seized, but an official at Greece's Merchant Marine Ministry told Reuters in Athens that no such incident had been recorded.

The sharp increase in attacks at sea this year off the poor and chaotic country has been fuelled by a growing Islamist insurgency onshore - gun battles broke out again in Mogadishu on Wednesday - and the lure of multi-million-dollar ransoms.

Somali Prime Minister Nur Hassan Hussein told Reuters naval patrols would not stop piracy and appealed for more help to tackle criminal networks with links beyond his country.

While analysts say paying ransoms just exacerbates piracy, the owners of the Saudi supertanker Sirius Star have begun talks. The pirates seized the vessel after dodging international naval patrols in their boldest strike yet.

'We do not like to negotiate with either terrorists or hijackers. But the owners of the tanker, they are the final arbiters of what happens here,' Saudi Arabia's Foreign Minister Prince Saud al-Faisal said on Wednesday.

The Sirius Star was seized 450 nautical miles southeast of Mombasa, far beyond the gangs' usual area of operations. It was believed to be anchored near Eyl, a former Somali fishing village that is now a well-defended pirate base.

Tanker spotted

'Eyl residents told me they could see the lights of a big ship far out at sea that seems to be the tanker,' Aweys Ali, chairman of Somalia's Galkayo region, told Reuters by telephone.

The Sirius held as much as 2 million barrels of oil, more than a quarter of Saudi Arabia's daily exports, and had been heading for the United States via the Cape of Good Hope.

More of the world's big shipping firms are diverting their fleets via the Cape, experts say. There is little evidence big oil tanker firms carrying most of the world's crude are avoiding the Suez Canal, although many are very concerned about pirates.

Somali gunmen are believed to be holding about a dozen ships in the Eyl area and more than 200 hostages. Among those vessels is a Ukrainian ship loaded with 33 tanks and other weapons that was captured in another high-profile strike earlier this year.

Chinese state media said on Wednesday a Hong Kong cargo ship taken in September had been freed and all 25 crew were safe.

The Sirius Star was seized despite an international naval effort, including by NATO, to guard one of the world's busiest shipping routes. Warships from the United States, France, Russia and India are stationed off Somalia.

But experts say deep pessimism over the prospects of any peace process onshore, bitter memories of disastrous past interventions, and the need to put out fires elsewhere - from Afghanistan to Congo - have snuffed out any real will to act.

Given that the pirates are well armed with grenades, heavy machineguns and rocket-launchers, most foreign navies have steered clear of direct confrontation once ships have been hijacked, for fear of putting hostages at risk. In most cases, the owners of hijacked ships are trying to negotiate ransoms.

British Royal Navy Commodore Keith Winstanley, deputy commander of the Combined Maritime Forces in the Middle East, said coalition forces could not be everywhere.

'The pirates will go somewhere we are not,' he told shipping weekly Fairplay, part of Jane's Information Group. 'If we patrol the Gulf of Aden then they will go to Mogadishu. If we go to Mogadishu, they will go to the Gulf of Aden.' -- REUTERS

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