Iran's defence minister confirmed on Friday a Pentagon claim that two Iranian fighter jets fired on an unarmed US Predator drone in the Gulf last week.

"Last week an anonymous plane entered the space over the territorial waters of the Islamic Republic of Iran in the Persian Gulf area which, due to the timely, clever and decisive action of our armed forces, was forced to flee," Ahmad Vahidi was quoted on ISNA as saying.

"This instance and others before show that the Islamic Republic of Iran has the needed vigilance to monitor all movements and takes decisive and timely actions."

His comments came after the deputy chief of Iran's armed forces, Brigadier General Masoud Jazayeri, had implied the aerial shooting had taken place, quoted earlier on Friday by the the Revolutionary Guards' website.

Pentagon spokesman George Little said on Tuesday the Iranian Su-25 Frogfoot fighters fired at the drone on November 1 but did not hit it.

"They intercepted the aircraft and fired multiple rounds," Little said.

It was unclear whether the Iranians intended to warn off the unmanned drone but Little said: "Our working assumption is that they fired to take it down."

The drone was "never in Iranian airspace" and came under fire off the Iranian coast over international waters, Little said.

In a warning to Tehran, Little said the United States was prepared to safeguard its forces.

The confrontation threatened to derail diplomatic efforts to defuse a mounting crisis over Tehran's nuclear programme, amid a shadow war of cyber attacks, bombings and assassinations.

Tough new sanctions led by Washington are squeezing Iran's economy, while the United States and Israel are accused of staging cyber sabotage on Tehran's uranium enrichment plants.