Iran's supreme leader, Ayatollah Ali Khamenei, talks to a state television reporter after being discharged from a hospital in Tehran on Sept. 15.  (HO/Iranian Supreme Leader's Web site via AFP)

The Islamic State, the extremist Sunni Islamist group that has taken over much of Iraq and Syria, once appeared to be doing the impossible: Uniting America and Iran in their opposition to a common enemy.

While Iran was not mentioned in President Obama's speech on how to tackle the Islamic State, there was much speculation that the center of Shiite Islam's political world would have some kind of role. With its powerful military and interests in Iraq and Syria, it would certainly be a potent, though controversial, ally.

However, Iran was not present at meetings in Paris that sought to come up with some kind of coalition to fight the Islamist group. And it has certainly not, like some Arab states, agreed to take part in U.S.-led airstrikes against the extremists.

Now that Iran's supreme leader, Ayatollah Ali Khamenei, is out of the hospital (where he had been undergoing well-publicized prostate surgery), the Iranian response to the plan seems unequivocal: It will not only not be a part of it, but it opposes it.

Khamenei's official English-language Twitter account released a series of tweets Monday, excerpted from a post-hospital interview, that made it clear what he thinks of America's plan.

Most notably, Khamenei asserted  that the United States did indeed reach out to Iran for talks, despite reports that Washington was resisting calls for Tehran to be invited (the United States has not denied some kind of exchange with Iran).

Khamenei's remark that it was Foreign Minister Mohammad Javad Zarif who refused a U.S. plan may also surprise some: Zarif had generally appeared relatively open to international cooperation since taking office in August 2013. Khamenei also appears to reference the widespread belief, in Iran and elsewhere, that the United States aided and abetted the Islamic State during its formative stages.

It is possible that some kind of talks are going on behind the scenes, and Khamenei's very public rejection of the plan is for show. However, other evidence suggests that Khamenei's comments should be taken at face value. Over the weekend, for instance, an unnamed Iranian official spelled out Tehran's position in an interview with Al-Monitor's Iran Pulse.

“Iran doesn’t trust the U.S., this is something the leader said before, and today all our commanders agree on: The U.S. can’t be an ally of Iran, and Iran can’t fight under the command of the U.S.," the official explained, adding: "We will continue to fight our war our way."

For now, it appears that there are two parallel drives to destroy the Islamic State: One led by Washington, and one led by Tehran.