NEW DELHI – An Indian naval vessel sank a suspected pirate "mother ship" in the Gulf of Aden and chased two attack boats into the night, officials said Wednesday, as separate bands of brigands seized Thai and Iranian ships in the lawless seas.

The owners of a seized Saudi oil supertanker, meanwhile, negotiated for the release of the ship, anchored off the coast of Somalia.

A multinational naval force has increased patrols in the waters between the Arabian peninsula and the Horn of Africa, where pirates have grown bolder and more violent. The force scored a rare success Tuesday when the Indian warship, operating off the coast of Oman, stopped a ship similar to a pirate vessel described in numerous bulletins. The Indian navy said the pirates fired on the INS Tabar after the officers asked to search it.

"Pirates were seen roaming on the upper deck of this vessel with guns and rocket propelled grenade launchers," said a statement from the Indian navy. Indian forces fired back, sparking fires and a series of onboard blasts – possibly due to exploding ammunition – and destroying the ship.

They chased one of two speedboats shadowing the larger ship. One was later found abandoned. The other escaped, according to the statement.

Larger "mother ships" are often used to take gangs of pirates and smaller attack boats into deep water, and can be used as mobile bases to attack merchant vessels.

Last week, Indian navy commandos operating from a warship foiled a pirate attempt to hijack a ship in the Gulf of Aden. The navy said an armed helicopter with marine commandos prevented the pirates from boarding and hijacking the Indian merchant vessel.

Separate bands of pirates also seized a Thai ship with 16 crew members and an Iranian cargo vessel with a crew of 25 in the Gulf of Aden, where Somalia-based pirates appear to be attacking ships at will, said Noel Choong of the International Maritime Bureau's piracy reporting centre in Malaysia.

"It's getting out of control," Choong said.

Tuesday's hijackings raised to eight the number of ships seized this week alone, he said. Since the beginning of the year, 39 ships have been hijacked in the Gulf of Aden, out of 95 attacked.

"The criminal activities are flourishing because the risks are low and the rewards are extremely high," Choong said.

The pirates used to mainly roam the waters off the Somali coast, but now they have spread in every direction and are targeting ships farther at sea, according to Choong.

He said 17 vessels remain in the hands of pirates along with more than 300 crew members, including a Ukrainian ship loaded with weapons and the Saudi supertanker carrying crude worth more than $120 million Cdn.

The Sirius Star was anchored Tuesday close to Harardhere, the main pirates' den on the Somali coast, with a full load of two million barrels of oil and 25 crew members.

Asked about reports that a ransom had been demanded, Saudi Foreign Minister Prince Saud al-Faisal said Wednesday that the owners of the tanker "are negotiating on the issue." He did not elaborate.

He said "we do not like to negotiate with pirates, terrorists or hijackers." But he said the owners of the tanker are "the final arbiter" on the issue.

Saudi Arabia, the world's leading oil producer, has condemned the hijacking and said it will join the international fight against piracy.

Meanwhile, Britain's foreign minister said in Beirut on Wednesday that his country will lead a European operation against piracy as of next month.

David Miliband says a foreign and defence policy group will use European military naval assets to "disrupt and to tackle the scourge of piracy."

NATO has three warships in the Gulf of Aden and the U.S. navy's Bahrain-based 5th Fleet also has ships in the region.

But U.S. navy Cmdr. Jane Campbell of the 5th Fleet said naval patrols simply cannot prevent attacks given the vastness of the sea and the 21,000 vessels passing through the Gulf of Aden every year.

"Given the size of the area and given the fact that we do not have naval assets – either ships or airplanes – to be everywhere with every single ship" it would be virtually impossible to prevent every attack, she said.

The Gulf of Aden connects to the Red Sea, which in turn is linked to the Mediterranean by the Suez Canal. The route is thousands of kilometres and many days shorter than going around the Cape of Good Hope off the southern tip of Africa.