A Cambodian sailor from the trawler, which was headed from Oman to Yemen to deliver fishing equipment when it was hijacked, was rescued four days later by passing fishermen.

Noel Choong, who heads the IMB's piracy reporting center in Kuala Lumpur, said the IMB received a report on the mistake late on Tuesday from Bangkok-based Sirichai Fisheries, which owned the Ekawat Nava5 vessel.

"We fired in self-defense. There were gun-toting guys with RPGs on it"

Commander Nirad Sinha, Indian navy spokesman

He said the company discovered the deadly mistake after speaking to the Cambodian sailor who was recuperating in a hospital in Yemen.

"The Indian navy assumed it was a pirate vessel because they may have seen armed pirates on board the boat which has been hijacked earlier," said Choong.

"We are saddened with what has happened. We hope that this incident won't affect the anti-piracy operation by the multi-coalition navies there."

In New Delhi, Commander Nirad Sinha, an Indian navy spokesman, said the ship had apparently been hijacked by pirates and that the frigate was responding to the threat to attack.

The Indian warship was part of an international
sea patrol in the Gulf of Aden [AFP]
"In so far as we are concerned, both its description and its intent were that of a pirate ship," he said on Wednesday.

"Only after we were fired upon did we fire. We fired in self-defense. There were gun-toting guys with RPGs [rocket-propelled grenade launchers] on it."

There have been 96 pirate attacks so far this year in Somali waters, and 15 ships with nearly 300 crew members were being held hostage by pirates who are demanding millions of dollars in ransom.

An international naval force deployed to patrol the seas of Somalia and the Gulf of Aden has been escorting some merchant ships and responding to distress calls in the area.

Shipping firms have also called for aggressive military approach to tackle piracy off Somalia's coast and prevent costly re-routing of vessels.