As per the Wall Street Journal, the mystery letter focused on the US-Iran imparted hobbies in battling the Takfiri activists.
The Journal refered to individuals advised on the letter, yet included that White House authorities declined to examine the letter with the daily paper.
"Organization authorities didn't deny the letter's presence when addressed by remote representatives lately," it said.
Because of news people's inquiries, the White House just said it talked about ISIL's danger with Iran on the sidelines of atomic talks in the middle of Tehran and the P5+1 gathering of nations.
White House representative Josh Earnest said, "I'm not in a position to examine private correspondence between the president and any world pioneer."
The ISIL terrorists, who were at first prepared by the CIA in Jordan in 2012 to destabilize the Syrian government, now control substantial swaths of region in Iraq and Syria.
They have debilitated all groups, including Shias, Sunnis, Kurds, Christians, Izadi Kurds and others, as they proceed with their outrages in Iraq and Syria.
US warplanes have been directing airstrikes against ISIL in Iraq since ahead of schedule August. Some Western states have additionally taken part in a portion of the strikes in Iraq.
Since late September, the US and some of its Arab associates have been doing airstrikes against ISIL inside Syria without any approval from Damascus or an UN command.
Ayatollah Khamenei has said that endeavors by the US and its associates against ISIL are not authentic and that gatherings like ISIL and al-Qaeda were made to face Iran and manage the wave of Islamic arousing in the Middle East and Africa.
The Leader has said the US-headed coalition is utilizing ISIL as a device to make divisions among Muslims, approaching Shia and Sunni Muslims not to get included in any move that will play into foes' hands.
"Shias and Sunnis shouldn't help the adversary by contaminating their sacred natures and inciting each other's estimations," Ayatollah Khamenei said a month ago.