In an interview broadcast on Sunday on CBS "Face the Nation" program, US President Barack Obama declined to comment on a report claiming that he sent a letter to the Leader about combating the Islamic State militant group, but said the United States and Iran shared a "common enemy" in IS.
Obama also said the nuclear talks between Iran and the major powers were not connected to the fight against Islamic State, also known as ISIL. "We're not coordinating with Iran on ISIL."
The Wall Street Journal claimed on Thursday that Obama sent a letter to the Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei last month describing their shared interests regarding the Islamic State in Iraq and Syria.
Ali Akbar Velayati, a senior advisor to the Leader, said on Sunday he was not informed about such a letter.
Iran has announced it is helping the Iraqi government and the Kurdistan Regional Government in their campaign against IS militants mainly through providing military advice. Tehran has also said it will not cooperate with the US on IS.
Ayatollah Khamenei on September 15 said Iran had refused a US invitation to cooperate in fighting the terrorist group.
"The American ambassador in Iraq asked our ambassador for a session to discuss coordinating a fight against Daesh (Islamic State)," IRNA quoted him as saying.
"Our ambassador in Iraq reflected this to us, which was welcomed by some officials, but I was opposed. I saw no point in cooperating with a country whose hands are dirty and intentions murky."
He said it was Iran's choice not to work with the United States.
In response to a question about the alleged secret letter, US Secretary of State John Kerry told reporters in Beijing on Saturday, "No conversation, no agreement, no exchange, nothing, has created any kind of deal or agreement (between Iran and the US) with respect to any of the events that are at stake in the Middle East."
He also said, "There is no linkage whatsoever of the nuclear discussions with any other issue, and I want to make that absolutely clear."
