According to the UK's *The Telegraph*, Iran has expressed "optimism" regarding the acquisition of Russia's S-400 air defense system. Reports indicate that Mohsen Rezaei, security chief to Iran's Supreme Leader Mojtaba Khamenei, traveled to the Kremlin on Thursday to deliver a handwritten letter. The core demand of the visit was securing the air defense system, with both sides also discussing issues such as the construction of a new natural gas pipeline.