An Indian fisherman has been killed and three seriously injured after an American naval ship fired on the small motorised boat in which they were travelling off the coast of Dubai.

The Emirates’ state news agency citing a foreign ministry official confirmed the incident, which took place about 48 kilometers off the Jebel Ali port, southwest of Dubai. The U.S. naval activity in this area has been stepped up after tensions with Iran have recently escalated over free passage along the strategic Strait of Hormuz, through which nearly 20 per cent of the world oil supplies pass.

The fisherman who was killed has been identified as Sekar of Periyapattinam in Ramanathapuram district of Tamil Nadu. The injured are Muniraj, Panpuvan and Murugan who also hail from Ramanathapuram, according to Karaiyur Fishermen Association President Malairajan.

Diplomatic sources said that their immediate task is to look at the “humanitarian side” of the incident, before investigating in greater depth the circumstances that led to the tragedy.

In a statement, the Bahrain based US fifth fleet that coordinates all activities of its warships in the region said that one of its ships fired as a means of last resort, after all warnings to stop the boat went unheeded.

"An embarked security team aboard a US navy vessel fired upon a small motor vessel after it disregarded warnings and rapidly approached the US ship near Jebel Ali," it said.

"The USNS Rappahannock used a series of non-lethal, preplanned responses to warn the vessel before resorting to lethal force," the statement observed.

"The US crew repeatedly attempted to warn the vessel's operators to turn away from their deliberate approach," it added. "When those efforts failed to deter the approaching vessel, the security team on the Rappahannock fired rounds from a .50-calibre machine gun."

There has been a steady buildup of U.S. warships in the Gulf following growing tensions between Washington and Tehran over its nuclear programme.

The U.S. had already deployed the USS Abraham Lincoln and the USS Enterprise – two aircraft carriers in this zone. On Monday, the Pentagon confirmed that a third aircraft carrier, USS John-Stennis, was being added to the existing fleet, further bolstering the U.S. naval presence in the Gulf.