A 677-foot United States Navy refueling ship in the Persian Gulf opened fire on Monday with a .50-caliber machine gun on what appeared to be a 30-foot sport fishing boat after it ignored repeated warnings to stop, killing a crew member and causing a spike in oil prices that reflected the heightened tensions in the region between Iran and the United States.

The United States Fifth Fleet command in Bahrain said in a statement that the shooting took place near the coast of the United Arab Emirates, a close American ally. The statement did not specify whether there were casualties or identify the nationality of the smaller vessel. But an American defense official said one person was dead, and the official news agency of the United Arab Emirates identified the victim as an Indian fisherman. At least three other Indians aboard were wounded, the agency said.

The encounter, which the Fifth Fleet command said was under further investigation, came against a backdrop of increasingly belligerent warnings from Iran against a buildup of naval forces in the area by the United States, which considers the free flow of oil from the Persian Gulf a vital national interest. The tensions have grown this month because of new Western sanctions aimed at stifling Iran’s oil exports.

The larger vessel’s response also appeared to reflect heightened awareness of the potential threat of small powerboats piloted by suicide attackers, such as the one that blew a 40-foot hole in the side of the Navy destroyer Cole in October 2000 while it was refueling in the Yemeni port of Aden, killing 17 sailors.

The news of the shooting on Monday, along with reports over the weekend that Iran planned to increase its military presence around the Strait of Hormuz, a vital oil transit route at the Persian Gulf’s entrance, lifted international oil benchmark prices by as much as $2 a barrel on Monday.

The Fifth Fleet said the encounter happened near the Emirates port of Jebel Ali, a docking point for American naval vessels about 30 miles southwest of Dubai.

“An embarked security team aboard a U.S. Navy vessel fired upon a small motor vessel after it disregarded warnings and rapidly approached the U.S. ship near Jebel Ali,” Lt. Greg Raelson, a spokesman for the Fifth Fleet, wrote in an e-mailed statement.

“In accordance with Navy force protection procedures, the sailors on the U.S.N.S. Rappahannock used a series of nonlethal, preplanned responses to warn the vessel before resorting to lethal force,” he said in the statement. “The U.S. 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-caliber machine gun.”

Lieutenant Raelson did not immediately provide further details.

Defense officials said the Navy crew’s efforts to warn away the vessel, which appeared to be a pleasure craft, included firing several warning shots.
The Rappahannock is a fleet replenishment oiler, used to refuel other naval vessels at sea. The Web site of the Navy’s Military Sealift Command described it as 677 feet long and 97 feet wide, with a regular crew of 84, of whom 81 are civilian mariners; the embarked security team would be in addition to the regular crew.

The Associated Press reported from Dubai that the smaller boat could have been mistaken for a threat in the gulf waters off Dubai, which are not far from Iran’s maritime boundaries.

The smaller vessel docked after the episode in a small Dubai port used by fishermen, and dozens of police officers and Emirati officials crowded around it, The A.P. reported, describing the vessel as a white-hulled civilian craft about 30 feet long, powered by three outboard motors. Similar boats are used for fishing in the region. Iran’s Islamic Revolutionary Guards Corps also uses relatively small, fast-moving craft in the Persian Gulf.
Rick Gladstone reported from New York, and Elisabeth Bumiller from Washington. Clifford Krauss contributed reporting from Houston.