Iran's Supreme Leader, Ali Khamenei, conditionally endorsed the nuclear agreement reached between Iran and six major world powers in July.  In a letter to addressed to President Hassan Rouhani on October 21, Khamenei specified nine conditions for the implementation of the deal. 

Specifically, the modification of the Arak heavy water reactor and Iran's exchange of enriched uranium for yellowcake will not begin until the International Atomic Energy Agency closes the case on the "possible military dimensions" of Iran's nuclear program.  The Supreme Leader also called upon the Supreme National Security Council to study and develop a plan for Iran's nuclear industry to achieve 190,000 SWUs (Separative Work Units enrichment capacity) over the next 15 years.

The Supreme Leader's letter comes after Iran's Parliament and Guardian Council both approved the agreement earlier in October.