An Iranian fighter jet tried to intercept a U.S. Predator drone over the Gulf but backed off after encountering two American military aircraft, the Pentagon said Thursday, according to AFP.
No shots were fired in the confrontation Wednesday, officials said, but the United States renewed a vow that it would protect its forces in the region.
The Pentagon initially said one of the U.S. aircraft discharged a flare as a warning to the Iranian plane but officials later said no flare was let off.
The incident, which the Pentagon said took place over "international waters," highlighted the tensions between the two arch-foes and the risks of an accidental clash escalating into a serious crisis.
At one point the Iranian F-4, an old U.S.-built warplane dating from the Vietnam War era, was within 16 miles of the unmanned Predator drone, spokesman George Little said, according to the AFP report.
The unarmed Predator, the workhorse of America's fleet of robotic planes, was carrying out "a routine classified surveillance flight" over the Gulf when it was approached by the Iranian warplane, he said in a statement.
In November, an Iranian fighter jet fired at a Predator plane, provoking a strongly-worded protest from the United States.
As after the November incident, the Pentagon warned it would keep up surveillance flights over what it deems international waters and to safeguard U.S. forces in the region.
Little said that "we reserve the right to protect our military assets as well as our forces and will continue to do so going forward."
Iran later accused the United States of carrying out "illegal and provocative acts" in the Persian Gulf and Sea of Oman, including repeated violations of Iranian airspace.
In December 2011, the Iranians captured a sophisticated Sentinel spy drone after it crashed on Iranian territory, in an embarrassment for Washington.
The United States expanded its military presence around the Gulf over the past year, deploying minesweepers and F-22 fighters to the area.
This came after Iran threatened to block the strategic Strait of Hormuz in retaliation for tough international sanctions imposed over its nuclear program.