WASHINGTON >> In a rare outreach to Iran’s Supreme Leader Ayatollah Ali Khamenei, President Barack Obama has written a letter about the fight against Islamic State militants, a common enemy in Syria and Iraq, according to diplomatic sources.

The U.S. and Iran are each engaged in military efforts to degrade the Islamic State group, essentially putting the longtime foes on the same side in the campaign against the extremists. However, the Obama administration has repeatedly insisted that it is not coordinating and will not coordinate its military actions with Iran, though officials from both countries have discussed the matter more broadly.

Obama’s letter to Iran’s powerful religious leader comes against the backdrop of the looming Nov. 24 deadline in nuclear negotiations between the U.S. and Iran, as well as five other world powers. While Obama has previously sent letters to Khamenei, any communication between the two men has been extremely rare.

The Wall Street Journal, which first reported that Obama had sent the letter, said it described a shared interest between the U.S. and Iran in fighting the IS and stressed that any cooperation on that would be largely contingent on Iran agreeing to the nuclear deal. However, while not confirming or denying the existence of the letter, administration officials said there were still no plans to cooperate or coordinate with Iran against the militants.

“The United States will not cooperate militarily with Iran in that effort,” White House spokesman Josh Earnest said. “We won’t share intelligence with them.”

Diplomatic sources separately confirmed the existence of the letter to The Associated Press. They did so only on the condition of anonymity to publicly discuss Obama’s outreach.

Obama authorized a U.S.-led air campaign against Islamic State fighters in Iraq in August and expanded the mission the following month to neighboring Syria. The U.S. is taking action alongside several other nations, including a handful of regional partners.

Iran is not part of the U.S. coalition, but it has also been fighting the IS on the ground. However, Iran’s interests in pursuing the Islamic State’s defeat differ from those of the Obama administration. Iran is a staunch supporter of Syrian President Bashar Assad, who is a target of the militants and opposed by the U.S.

Two chief critics of Obama’s foreign policy, GOP Sens. John McCain of Arizona and Lindsey Graham of South Carolina, called it “outrageous” that Obama would seek to enlist Iran in its fight against the IS given Iran’s support for Assad and Shia extremists throughout the region.

“The consequences of this ill-conceived bargain would destroy the Syrians’ last, best chance to live in freedom from the brutal Assad regime,” the two senators said in a joint statement.

U.S. officials have not ruled out the possibility that a nuclear accord with Iran could open the door to discussions on other issues, but they have sought to keep the delicate negotiations focused solely on Tehran’s disputed nuclear program. The U.S. and its negotiating partners say Iran is pursuing a bomb, while Iran says its nuclear program is for peaceful purposes.

The prospects for a final agreement remain uncertain, with Obama saying on Wednesday that the ability to secure a deal is an “open question.”

The technical details of the talks have been closely guarded by the negotiating partners — the U.S., Britain, China, France, Germany, Russia and Iran. The broad parameters of a potential agreement include Iran cutting back on its number of centrifuges enriching uranium and redesigning a planned heavy water reactor so it doesn’t produce plutonium. Both materials can be used in nuclear warheads.

In exchange, the U.S. in particular would have to roll back some of the financial, trade and oil sanctions that significantly cut off Iran from global markets.

The U.S. and Iran broke off diplomatic relations in 1979 after the Islamic revolution and the storming of the U.S. Embassy in Tehran, where 52 Americans were held hostage for more than a year. However, the relationship began to thaw after Obama took office, particularly following the election last year of a more moderate-sounding Iranian president, Hassan Rouhani.

U.S. and Iranian officials held a series of secret meetings last year that ultimately paved the way for the resumption of international nuclear negotiations. Obama and Rouhani also held a historic phone call last fall, the first direct communication between their nation’s leaders since the Islamic revolution.

However, the two men have not spoken since and skipped the opportunity to meet while attending U.N. General Assembly meetings in New York in September.

Despite Rouhani’s standing as president, U.S. officials believe Khamenei, the powerful supreme leader, has the ultimate say in whether Iran reaches a nuclear deal with world powers.