The Indian authorities have taken up the killing of two Indian fisherman on Wednesday by the security personnel on board the Italian cargo vessel Enrica Lexie seriously and has decided to register a case against the crew responsible for the crime.

Two fishermen from Kerala and Tamil Nadu were shot dead by the Italian security personnel on board an Italian merchant vessel in the Arabian Sea off Kerala, mistaking them as pirates.

"Our understanding is we know these are fisherman who were fired upon and two of them were killed. This was in Indian territorial waters," Reuters quoted an official, who declined to be named. "Their understanding seems to be that it was pirates and so shot at them mistakenly or otherwise," he added.

The Italy's Navy alleged that the fishing boat approached their vessel in an aggressive manner.

"The Navy security team on the Enrica Lexie intervened to avert an attempted attack by armed personnel from another vessel," a Navy press release said. "The Navy team on the mercantile ship used standard procedures. The fishing vessel distanced itself after the third series of warning shots that were made without evident damage to the vessel," it added.

However, Home Secretary R.K. Singh said that a case will be registered against the people responsible for the killing of the two Indian fishermen and that "law will take its own course".

Defence Minister A.K. Antony described the incident as "very serious" and unfortunate. He said that Kerala Police and the Indian Coast Guard are investigatin on the matter. He added that India will maintain strict vigil to ensure such incident don't repeat in the future.

Indian security personnel on the coast said that the Italian vessel was in Indian waters where they were prohibited from carrying weapons.

(Inputs from Reuters)