Iran has warned the United States that it will react strongly against any intrusion by Washington into its airspace, local media reported.
Sunday's warning comes 10 days after two Iranian warplanes shot at a US drone.
"Yes, we opened fire, and it was with warning shots. If they do it again they can expect an even stronger response," the Iranian Students News Agency quoted General Amir-Ali Hadjizadeh, head of the elite Revolutionary Guards air and space forces, as saying.
Hadjizadeh was reported as saying on Sunday: "This spy drone entered Iranian airspace and had to turn around because of the immediate reaction by fighters of the Revolutionary Guards".
On Friday, Ahmad Vahidi, Iranian defence minister, confirmed the incident, saying the drone had "entered the space over the territorial waters of the Islamic Republic of Iran in the Persian Gulf area".
George Little, Pentagon spokesman, said on Thursday the Iranian Su-25 Frogfoot fighters fired at the robotic Predator drone on November 1 but did not hit it.
The US drone was "never in Iranian airspace" and came under fire from the fighter jets off the Iranian coast over international waters, Little said."They intercepted the aircraft and fired multiple rounds," he said.
In a warning to Tehran, the Pentagon spokesman said the United States was prepared to safeguard its forces.
"We have a wide range of options, from diplomatic to military, to protect our military assets and our forces in the region and will do so when necessary," Little said.
Hadjizadeh added that the US unmanned aircraft had been "flying over Kharg island to gather information about economic activity on the island, and the arrival and departure of oil tankers".
Kharg, 25 kilometres off the Iranian mainland, is the Islamic Republic's main export terminal for its oil.
The November 1 drone incident came less than a week before the US presidential election, but the Pentagon kept it quiet until reports of the confrontation leaked out.