'Intervention must be in place very soon, as in this week,' says Philip Jenkins, Distinguished Professor of History in Baylor’s Institute for Studies of Religion, who frequently authors op-ed pieces in The Wall Street Journal, The Washington Post and New Republic. 'Iranian personnel are already in the country (Iraq), but they would benefit immensely from US support, especially air support.'

'The only power in the (Middle East) neighborhood with the ability to stop the advance of ISIS (the Islamic State of Iraq and Syria) - and mass murder across Iraq - is Iran,' Jenkins said. 'And I would be extremely surprised if that US-Iranian cooperation was not already in place, and it will become more obvious in the coming weeks.'

He predicted that major military supplies will reach Iran very soon 'through middlemen contractors not overtly tied to the US.'

In the Iran-US hostage crisis from 1979 to 1981, 66 American diplomats and citizens were held hostage for 444 days, but today Iran is 'our enemy’s enemy,' and US-Iran cooperation is 'necessary. It’s essential,' Jenkins said.

'The problem is that it may well not be legal, given the network of restrictions and sanctions that the West has imposed upon Iran. Saving Iraq might be possible, but politically, it is very risky indeed.'

Kerry told Yahoo! News that Washington was open to discussions with Iran and that he would “not rule out anything might be constructive.' But he said contacts with Iran would be 'step by step.'

Former deputy CIA director Mike Morell, meanwhile, has said that partnering with the Iranians would not be in the best interests of the United States.