"We are taking this issue very seriously. What happened was against the laws and the norms. The guilty will have to be punished," Defence Minister A K Antony told reporters here.
Underlining that India wanted to send "strong signals" on the issue, the minister said, "This is not only for India but for all others. Everybody should follow the norms and the laws."
He was asked about the steps being taken by the government to book the guilty in the incident.
Antony said the Kerala police and the Indian Coast Guard were questioning all the people involved in the case and it would be "inappropriate" for him to comment further on the incident.
The two fishermen, native of Alappuzha, were killed on Wednesday night when armed guards on-board the Italian merchant vessel Enrica Lexie opened fire on their fishing boat.
The vessel was brought to Kochi early today and police and Coast Guard personnel were questioning the crew. The ship has been berthed at Kochi oil terminal, where security has been tightened.
The preliminary assessment of the marine authorities is that the armed guards aboard the ship might have fired at the fishing boat mistaking it for a vessel belonging to pirates.
Italian Consul General in India, GiamPaolo Cutillo, was in Kochi yesterday in connection with the incident and had met the city Police Commissioner there.
Inspector General S P S Basra, Regional Commander of Coast Guard Region (West), said in Kochi that the Italian vessel had not reported the incident.
It was the coastal police at Neendakara in Kollam district which reported the incident to the Coast Guard and, thereafter, search operations were launched, he told reporters.
The vessel was in the Indian Exclusive Zone when the incident occurred, he said.
"It was an error of judgement on the part of the vessel", he said but firing on unarmed fishermen could not be justified.
"They (the Italian vessel's crew) had taken some time to accept the case. An FIR has been registered and the police were investigating the case," he said, when asked about the reported delay in taking action against the erring ship.
On the explanation by the Italian vessel crew that the guards had opened fire suspecting the fishermen to be pirates, he said, "Any incident of piracy has to be immediately reported to the Coast Guard. They have not done it. They gave the information over two-and-a-half hours later", Basra said.
The Italian ship has stated that the crew had sighted a "suspicious" boat off Alapuzha on February 15 at about 1600 hours and that it was closing in from a distance of at 2.8 nautical miles.
The boat was "warned" by flashing of search lights and displaying of the weapons but it continued to close in and got up with a 100 metre range from the ship, they have said, claiming that the security team of the ship sighted six persons and fired warning shots.
The crew informed the owners and activated the 'ship security alert system', they have claimed.
The coastal police has registered a murder case against the crew of the vessel based on the evidence of bullet injuries found on the bodies of the dead fishermen -- Valentine alias Jelestine (45) and Ajesh Binki (25)-- during post-mortem.