The United States has deployed a fleet of robot subs in the Gulf to prevent Iran from blocking the strategic Strait of Hormuz with mines in the event of a crisis, officials say.
The "SeaFox" drone "has been deployed in the Fifth fleet AOR," which includes the Gulf and the Arabian Sea, a Navy official told AFP news agency on Thursday, confirming information first reported in the Los Angeles Times newspaper.
The undersea drone, about four feet (1.2 meters) long and equipped with a camera and sonar, is guided by a cable from a ship.
German manufacturer Atlas Electronik says the drone has a range of about 3,200 feet (1,000 metres) and carries an explosive to destroy mines.
Fears of a closure of the Straight of Hormuz -- through which about a fifth of the world's traded oil passes -- intensified earlier this year after Iran threatened to close it if Western governments kept up efforts to rein in Tehran's controversial nuclear programme by choking off its oil exports.
In response, the US military has been bolstering its presence in the region.
It sent four mine sweeper ships in early June, joining four other mine sweeping vessels already in the region, according to the Fifth Fleet.
The Navy also has MH-53 Sea Stallion helicopters and USS Ponce, an old amphibious warship that has been converted into a "floating base," stationed in Bahrain, home to the Fifth Fleet headquarters.
And in late April, a squadron of F-22 stealth fighters was sent to the Al Dhaafra Air Base in the United Arab Emirates.
Iran has an arsenal of about 2,000 sea mines that can be laid by any one of its dozen submarines or its many speed boats.