An Indian fisherman on board the boat that came under fire from an American naval vessel off the Dubai coast, resulting in the death of one of his Indian colleagues, said on Tuesday the crew received no warning.
India has asked the US to take action.
"We are in touch with our envoys in Dubai and the US and have instructed them to take it up with the respective governments... The UAE government has already filed a case," external affairs minister SM Krishna said.
US ambassador to India, Nancy Powell, called foreign secretary Ranjan Mathai to convey her regret and to say Washington would investigate the matter.
The US maintains the fishing boat "disregarded non-lethal warnings and rapidly approached the US ship".
Pentagon Press Secretary George Little told reporters that the USNS Rappahannock escalated warning measures to -- in response to a potential threat posed by this vessel. "The incident remains under investigation. And this is something that all US Navy ships take into account for security reasons."
When pressed further if the US will apologise for the loss of life, Little said, "We certainly regret the loss of life in this incident. There were, in fact, warning measures that were taken based on what we know now. We'll know the full facts of this incident once that investigation is complete."
The deceased, Sekhar, hails from Tamil Nadu's Ramanthapuram district. His colleagues Muniraj, Panpuvan and Murugan, from the same district, were seriously injured when the USNS Rappahannock fired on their boat on Sunday night.
Four other crew members - two Indians and two Emiratis - were unhurt. Indian consular officials have met the wounded.
"He says there was no warning," Indian ambassador to the UAE, MK Lokesh, told AP, reporting what one of the survivors told him.
Dubai's police chief, Lt Gen Dahi Khalfan Tamim, said initial investigation suggests "the boat was on its right course and did not pose any danger".
In a similar incident, on February 2, two fishermen were shot dead off the Kerala coast by Italian marines on board a merchant ship, who mistook them for Somali pirates.
(With AP inputs)