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The Indian warship INS Tabar, shown in a file photo, opened fire Wednesday on a pirate vessel. ((Indian Navy/Associated Press))

An Indian warship was able to fight off and destroy a suspected Somali pirate vessel, the navy said on Wednesday, the same day two other ships were hijacked off the coast of Somalia.

Meanwhile, the owners of a seized Saudi oil supertanker were reportedly negotiating for the release of the ship, anchored off the coast of Somalia.

The pirates had threatened to blow up the INS Tabar after Indian officers asked the pirate vessel to stop on Tuesday to be searched in the Gulf of Aden, the Indian navy said. Officials said they had also spotted pirates with rocket-propelled grenade launchers on the vessel.

The pirate vessel then opened fire on the Indian ship, which, according to GlobalSecurity.org, is a 122-metre vessel, carrying cruise missiles, surface-to-air missiles and six-barreled 30-mm machine guns for close combat.

"INS Tabar retaliated in self-defence and opened fire on the mother vessel," the navy said in a statement.

"Explosions were heard, possibly due to exploding ammunition that was stored on the vessel," the navy said, adding that the vessel then sank.

The Indians chased one of two speedboats accompanying the pirate vessel. The speedboat was later found abandoned. The other speedboat escaped, according to a navy statement.

The attack came the same day a Thai fishing boat with 16 crew members and an Iranian cargo ship with a crew of 25 were also hijacked in the Gulf of Aden.

Hijacked supertanker anchored off Somalia

Also Tuesday, pirates who hijacked a Saudi-owned supertanker anchored the vessel off the north coast of Somalia. The Sirius Star was anchored near Harardhere, 425 kilometres from Eyl. It is loaded with two million barrels of crude oil valued at around $100 million.

The ship, with 25 crew members on board, was seized over the weekend by Somali pirates, 830 kilometres off the Kenyan coast.

Saudi Foreign Minister Prince Saud al-Faisal said Wednesday that the owners of the tanker "are negotiating on the issue" of a ransom but wouldn't 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.

Noel Choong, who heads the International Maritime Bureau's piracy reporting centre in Kuala Lumpur, said a total of 17 vessels are currently being held hostage in Somali waters with more than 300 crew members.

"It's getting out of control," Choong told the Associated Press.

Choong said eight ships have been hijacked this week. Since the beginning of the year, 39 ships have been hijacked in the Gulf of Aden, out of 95 attacked.

"There is no firm deterrent, that's why the pirate attacks are continuing," Choong said. "The criminal activities are flourishing because the risks are low and the rewards are extremely high."

Pirates have generally released ships they have seized after ransoms are paid.

With files from the Associated Press, Reuters