US Secretary of State John Kerry says the Obama administration is willing to hold talks with Iran over deteriorating security conditions in Iraq.
Mr Kerry is not ruling out potential US-Iranian military co-operation in stemming the advance of Sunni extremists.
He also said US drone strikes “may well” be an option.
In a Monday interview with Yahoo! News, Mr Kerry said Washington is “open to discussions” with Tehran if the Iranians can help end the violence and restore confidence in the Iraqi government.
Asked about possible military co-operation with Iran, Mr Kerry said he would “not rule out anything that would be constructive”.
However, he stressed that any contacts with Iran would move “step-by-step”.
US officials said earlier there is a possibility that a senior American diplomat may discuss Iraq with an Iranian delegation at nuclear talks in Vienna.