U.S. Secretary of State John Kerry
U.S. Secretary of State John KerryReuters

US Secretary of State John Kerry has waffled on his position from last Friday, when he ruled out Iran's participation in a global coalition against Islamic State (ISIS) - on Monday, he said in an interview that he would be open to military cooperation with Iran.

Asked in a Yahoo interview whether the US would cooperate militarily with Iran, Kerry did not rule out the option, saying "let’s see what Iran might or might not be willing to do before we start making any pronouncements."

Kerry elaborated saying "I think we are open to any constructive process here that could minimize the violence, hold Iraq together - the integrity of the country - and eliminate the presence of outside terrorist forces that are ripping it apart. I wouldn’t rule out anything that would be constructive to providing real stability.

The Yahoo interview can be seen here:

The comments come as Iranian Supreme Leader Ayatollah Khamenei said Monday that he had rejected a US proposal to cooperate against ISIS.

"The American ambassador in Iraq asked our ambassador (in Iraq) for a session to discuss coordinating a fight against Islamic State,” Khamenei said according to the state news agency IRNA.

Responding to Khamenei, Kerry said Monday "I'm not going to get into a back and forth. I don't want to do that. I don't think that is constructive, frankly."

Asked whether Khamenei's claim that he was invited to join the US in military action, Kerry said "I have no idea of what interpretation they drew from any discussion that may or may not have taken place. We are not coordinating with Iran. Period."

Two weeks ago it was reported that Khamenei had authorized his army to coordinate joint military operations with the US against ISIS in Iraq. The State Department later clarified it has "no plans" for any military coordination with Iran in the fight against Islamic State.

Iran is currently engaged in a likely final round of negotiations with world powers over its nuclear program ahead of a November 24 deadline.

Israel has reported that the Islamic regime is continuing its nuclear program despite ongoing talks, warning it is "closer than ever" to obtaining a nuclear weapon. It has also warned against a rapprochement between the US and Iran over the Islamic State threat.