US President Barack Obama secretly wrote to Iran’s Supreme Leader Ayatollah Sayyed Ali Khamenei in the middle of last month and described a shared interest in fighting the so-called Islamic State militants in Iraq and Syria

US President Barack Obama secretly wrote to Iran’s Supreme Leader Ayatollah Sayyed Ali Khamenei in the middle of last month and described a shared interest in fighting the so-called Islamic State militants in Iraq and Syria, according to people briefed on the correspondence.

Obama stressed to Sayyed Khamenei that any cooperation on ISIL was largely contingent on Iran reaching a comprehensive agreement with global powers on the future of Tehran’s nuclear program by a Nov. 24 diplomatic deadline, the same people say. 

The October letter marked at least the fourth time Obama has written Iran’s leader since taking office in 2009 and pledging to engage with Tehran’s government.

“Obama’s letter also sought to assuage Iran’s concerns about the future of its close ally, President Bashar al-Assad of Syria,” according to another person briefed on the letter. It states that the U.S.’s military operations inside Syria aren’t targeted at President Assad or the Syrian army.