The US aircraft carrier Enterprise has been deployed to a strategic area that includes waters close to Iran.
The warship joins two carriers already in the Fifth Fleet area of operations and strengthens the US Navy's biggest presence in the Gulf since the first Iraq invasion.
'Enterprise provides navy power to counter the assertive, disruptive and coercive behaviour of some countries, as well as support our soldiers and marines in Iraq and Afghanistan,' a US Navy statement said.
In May, a flotilla of US warships sailed through the narrowest point in the Gulf to hold exercises off Iran's coast in a major show of force.
Tension over Tehran's nuclear ambitions has raised regional fears of a military confrontation, although one Navy spokeswoman insists Iran is not a specific target.
'These operations are not specifically aimed at Iran. We consider this time unprecedented in terms of the amount on insecurity and instability in the region," Navy spokeswoman Denise Garcia said, citing Somalia, Lebanon, Iraq and Afghanistan.
The Fifth Fleet's area of operations includes the Gulf, the Arabian Sea, the Red Sea, the Gulf of Aden, the Gulf of Oman and parts of the Indian Ocean.