The United States Navy has fired on a small motor boat which was deliberately and rapidly approaching one of its vessels off the coast of the United Arab Emirates on Monday.
The Navy says crew on the USNS Rappahannock, a fuel supply ship, repeatedly warned those on the motor boat to turn away before opening fire with a 50-calibre machine gun.
There is no confirmation of casualties although a UAE official said an Indian fisherman had been killed and three more wounded.
It is not clear where the crew of the boat are from.
The US Navy's 5th Fleet is based in Bahrain.
The BBC reports the United States has increased its presence in the Gulf after Iran renewed threats to close the Strait of Hormuz.