"We have indications that they did indeed fly air strikes with F-4 Phantoms in the past several days," Rear Admiral John Kirby told AFP.
The US Department of Defense also commented on the issue on Twitter, saying "[w]e have no indication that reports are not true."
In another tweet the agency added that it is "not taking a position on these particular reports regarding these particular strikes."
"We are not taking a position on these particular reports regarding these particular strikes," says @PentagonPresSec re: Iran, airstrikes— U.S. Dept of Defense (@DeptofDefense) 2 декабря 2014
Kirby stressed that the United States and Iran are not coordinating their efforts. "We are flying missions over Iraq. We coordinate with the Iraqi government as we conduct those. It’s up to the Iraqi government to deconflict that air space," a Pentagon spokesman said, as quoted by AFP. "Nothing has changed about our policy of not coordinating military activity with the Iranians," he added.
Iran, a country where Shia Muslims make up the majority of the population, has for months assisted Iraqi security forces and Shia militias on the ground in their fight against the radical Sunnis. However, it is the first time the US has confirmed that the Islamic Republic has conducted airstrikes against the IS.
The US-led international coalition conducted 27 airstrikes on IS targets in Syria and 28 airstrikes in Iraq from November 28 to December 1, the Pentagon said in a news release. The airstrikes are part of a campaign, dubbed Operation Inherent Resolve, aimed at destroying the radical Sunni group, currently controlling large swathes of land in Iraq and Syria.