The US and Iran insist that there is no direct field coordination between them in the war against the Islamic State in Iraq and the Levant (ISIL). This comes despite assertion by the US that Iran had launched airstrikes targeting ISIL sites in eastern Iraq in late November 2015, and Iran’s initial denial of the actions before ultimately confirming the reports. This paper looks into the nature of Iran’s denial, and uses this investigation to understand the US stance toward an Iranian role in the war against ISIL. This investigation comes in the context of the mid-October 2015 confidential messages sent by US President Barack Obama to Iran’s Supreme Guide Ayatollah Ali Khamenei, where Obama mentioned a “common interest” between the two countries in the fight against ISIL in both Iraq and Syria.