DUBAI: A US navy ship fired on a boat off the United Arab Emirates on Monday in the southern Gulf where tension has been rising after it ignored warnings, the navy said.

It gave no details on the outcome of the incident, which was being investigated, but US media reports said one person was killed and three were wounded.

“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,” an Emirati port city, the Bahrain-based Fifth Fleet said in a statement.

“The USNS Rappahannock used a series of non-lethal, preplanned responses to warn the vessel before resorting to lethal force,” it said.

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

The US navy has been building up its forces in the oil-rich region since tensions spiked with Iran in December over its nuclear programme, with Tehran threatening to possibly close the strategic Strait of Hormuz in the southern Gulf.

It has deployed two aircraft carriers to the region -- the USS Abraham Lincoln and the USS Enterprise -- and doubled its minesweeper fleet in the area from four to eight ships on June 23.

The deployment aims to send a clear message to Iran over its threats to mine the narrow Strait of Hormuz through which about a fifth of the world's traded oil passes.