- The planes weren't in Iranian airspace
- It's not the first such incident of late
The EP-3 and P-8 planes were in international airspace but "near Iranian airspace."
The Iranians made three radio calls to the two planes warning them not to enter Iranian airspace and risk being shot down with surface-to-air missiles, the official said.
"All three calls used threatening language," the US defense official said.
The US Navy crews knew they were flying "outside the known range of Iranian air defenses" and proceeded with their flight plans.
The American crews "responded in an appropriate and calm manner," the official said, adding that the crews identified their planes themselves as coalition aircraft flying in international airspace.
The two planes -- reconnaissance aircraft that routinely fly that flight pattern in the Strait of Hormuz -- were on separate flight plans, but close to each other.
Also, senior US military officials are trying to assess whether the number of incidents with the Iranians have increased or whether more incidents are simply being reported by US naval commanders in the region because of the sensitivity to Iranian incidents.