Iranian fighter jets have bombed Islamic State (IS) jihadists in eastern Iraq in recent days, but the strikes were not coordinated with US forces, the Pentagon says.
"We have indications that they did indeed fly air strikes with F-4 Phantoms in the past several days," Pentagon spokesman Rear Admiral John Kirby said.
His comments came after Al Jazeera recently ran footage of what appeared to be an F-4 fighter, similar to those used by the Iranian air force, attacking targets in the eastern province of Diyala.
At a press conference earlier, Rear Admiral Kirby said it was up to the Iraqi government to oversee and coordinate military flights by different countries and not US commanders.
"We are flying missions over Iraq. We coordinate with the Iraqi government as we conduct those. It's up to the Iraqi government to de-conflict that air space," Rear Admiral Kirby said.
"Nothing has changed about our policy of not coordinating military activity with the Iranians."
Iranian forces have reportedly been active on the ground in Iraq assisting Shiite militia and Baghdad government units, but this was the first time the US had confirmed the Iranians were conducting air strikes against IS.
Iran has also provided Sukhoi Su-25 aircraft to Iraq amid widespread speculation the planes were flown by Iranian pilots.
Confirmation of the Iranian air raids offers the latest illustration of how the threat posed by IS has brought the two arch-foes together in the fight against the jihadists.
Shiite-ruled Iran has close ties to the Shiite-led government in Baghdad, which has struggled to counter IS.
US fighters, bombers and surveillance aircraft fly daily missions over Iraq along with other coalition warplanes from European governments as well as Australia and Canada.
The US-led air war against IS began on August 8 in Iraq and was extended into Syria in September.