A report in "The Wall Street Journal" newspaper says U.S. President Barack Obama secretly wrote to Iran's Supreme Leader Ayatollah Ali Khamenei in October about fighting Islamic State (IS) militants in Iraq and Syria.
The newspaper reported on November 6 that Obama stressed in his letter that any cooperation was tied to an agreement being reached over Iran's nuclear program by November 24. The letter is at least the fourth time that Obama has written to Khamenei.
White House Press Secretary Josh Earnest declined to comment on the report and said the U.S. policy toward Iran "remains unchanged."
Earnest added that the U.S. will not cooperate militarily or share intelligence with Iran in the fight against IS militants.
However, he said that talks have occurred within the context of negotiations over Iran's nuclear program.
He said: "We have also discussed on the sidelines of those talks, on at least a couple of occasions, the ongoing campaign that is being conducted" against IS militants and more than 60 countries that are now part of a broad coalition against the Islamic militants in Iraq and Syria.
U.S. House Speaker John Boehner, a Republican from the state of Ohio, said in response to "The Wall Street Journal" report that he doesn't think the United States should be bringing Iran into the fight against IS militants.
Boehner said he does not trust the Iranians, and that he has doubts about whether negotiations between Iran and world powers on a permanent nuclear deal are "serious negotiations."
Obama is due to meet with congressional leaders and other lawmakers from both the Republican and Democratic parties on November 7 to discuss a new mandate from Congress for U.S. military action against IS militants in Syria and Iraq.
Those talks follow midterm elections on November 4 that saw Republicans take over majority control of the U.S. Senate from Democrats.
Obama has said that he would would work with the outgoing Congress "to right-size and update" the administration's war powers before the next Congress convenes in January.
Obama's administration has relied on 2001 and 2002 congressional authorizations for the current campaign.
Iran and the United States both oppose the Sunni-led IS militants -- although Tehran has criticized the U.S.-led international coalition that has been carrying out air strikes against the militants in both Iraq and Syria.
Iran denies sending combat troops into Iraq to fight the militants.
But Tehran has admitted that Iranian military advisers have been sent to Iraq and that Iran is helping with logistical support against IS militants.
With reporting by Reuters, "The Wall Street Journal," and AP