The Indian navy has said that one of its warships in the Gulf of Aden has destroyed a ship belonging to pirates operating off the coast of Somalia.
The Tabar opened fire on a pirate "mother ship" after it came under attack, a government statement said.
There has been a surge in piracy incidents off Somalia.
The Saudi-owned Sirius Star supertanker is currently anchored off the Somali coast after the vessel and its 25 crew were seized by pirates.
Vela International, operators of the Sirius Star, told the BBC no demands had yet been received from the pirates. The company also said all the crew were safe.
The biggest tanker ever hijacked, Sirius Star is carrying a cargo of two million barrels - a quarter of Saudi Arabia's daily output - worth more than $US100 million.
India is among several countries are already patrolling the Gulf of Aden, one of the world's busiest shipping lanes which connects the Red Sea and the Indian Ocean.
The Indian navy said the Tabar spotted a pirate vessel while patrolling 285 nautical miles south-west of Salalah in Oman, on Tuesday evening.
When it demanded the vessel stop for investigation, the pirate ship responded by threatening to "blow up the naval warship if it closed on her", the statement said.
The navy said the pirates on board were armed with guns and rocket propelled grenade launchers. They threatened to blow up the Tabar and then fired on it.
The Indians say they retaliated by opening fire and that there was an explosion on the pirate vessel, which sank.
Some of the pirates tried to escape on two speedboats - the Indian sailors gave chase but one boat was later found abandoned, while a second boat escaped.
The Tabar has been patrolling the Gulf of Aden since 23 October, and has escorted 35 ships safely during the "pirate-infested waters", the statement said.
Last week, an helicopter-borne Indian marine commandos stopped pirates from boarding and hijacking an Indian merchant vessel.