News of the letter, Obama's fourth to Khamenei since 2009, was shared Thursday by people briefed on the correspondence.
The letter was meant to reinforce the shared interest of Iran and the United States in defeating IS, as well as moving Iran closer to a deal on a nuclear agreement. Obama stressed cooperation in defeating IS was contingent on a comprehensive agreement to limit Iran's nuclear ambitions, as spelled out in negotiations between Iran and world powers. The negotiations have a diplomatic deadline of Nov. 24.
The letter suggests Obama sees Iran as crucial in the United States' plan to defeat IS, with either a constructive or negative role to play, the Wall Street Journal said Thursday.
"There's a sizable portion of the (Iranian) political elite that cut their teeth on anti-Americanism. Whether they can manage to say 'yes' is an open question," Obama said Wednesday.
He did not comment on his letter, and White House spokesman Josh Earnest said Thursday he could not confirm the letter.