An Indian warship destroyed a pirate ship in the Gulf of Aden as gunmen from Somalia seized at least two more vessels despite a large international naval presence off their lawless country.

The Indian navy said the pirates fired on the INS Tabar after the officers asked it to stop to be searched. Indian forces fired back, destroying the ship, and then chased one of the speed boats, which was later found abandoned. The other escaped, according to a navy statement.

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.

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

The Thai boat, with 16 crew members, was flying a flag from the tiny Pacific nation of Kiribati but operated out of Thailand. It made a distress call as it was being chased by pirates in two speedboats but the phone connection was cut off midway.

That followed the capture of a Hong Kong-flagged ship, with a crew of 25, which was 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 yesterday - and the lure of multi-million-dollar ransoms.

No ransom has been demanded so far for the Saudi supertanker Sirius Star, which the pirates seized after dodging international naval patrols in their boldest strike yet.

A spokesman for the owners, Saudi Aramco, said the company hoped to hear from the hijackers soon. One Somali website said the attackers were demanding $250 million.

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.

Somali gunmen are believed to be holding about a dozen ships in the Eyl area and more than 200 hostages.

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.

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. "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."

Questions:

1. What has been the pirates biggest capture?

2. Where was it seized?

3. How many ships and hostages are the Somali pirates holding?

Answers:

1. A Saudi supertanker, called Sirius Star, carrying $100 million of oil.

2. 450 nautical miles southeast of Mombasa.

3. Somali gunmen are believed to be holding about a dozen ships in the Eyl area and more than 200 hostages.