Iranian fighter jets shot at an unmanned US drone during a routine surveillance mission over the Gulf, Pentagon officials have said.
The defence department said the drone was not damaged in the incident, which it said took place in international air space on 1 November.
Pentagon spokesman George Little said the president had been informed.
Last year, the Iranians captured a US drone they said had invaded their air space and refused to give it back.
The Americans said the drone had malfunctioned.
After the latest incident, Mr Little said the US would continue surveillance in the area.
"The United States has communicated to the Iranians that we will continue to conduct surveillance flights over international waters over the Arabian Gulf," he said.
Mr Little insisted that the drone had never been into Iranian air space.
According to the Pentagon, two SU-25 jets intercepted the Predator drone and fired "multiple rounds".
They missed their target, and the drone was guided back to base.
Defence officials have a policy of not commenting on surveillance missions, but said they would give details this time because of media reports about the confrontation.