As the BRICs develop their aerospace industries, they will decide whether they will participate in the international trading system or sell to a bloc of client states. Unfortunately, Russia seems to be returning to familiar paths as it attempts to produce 4,500 aircraft by 2025. Russia’s state-owned UABC is selling several Tupolev 204s to the Islamic Republic’s state-owned Iran Air. U.S. and European sanctions on Iran prevent the airline from buying the spare parts needed to maintain its Boeing and Airbus fleets. The sanctions are in place to pressure Iran to drop its nuclear program.
By constricting the Iranian economy, the West may persuade the regime in Tehran to give up its expensive nuclear ambitions and open up to true wealth. Russia’s decision to sell to Iran–not only airplanes–undoes that work. Russia is expressing its disdain for the multilateral trading system and bucking up a state sponsor of terrorism, a force for regional instability, and one of its old Cold War clients.
Russia is allowing its need for an outlet for production of new jets to supersede its interest in a stable regional neighbor. Moscow’s course, while it may bring good business in some quarters, indicates the path Russian aerospace and commerce in general will take in coming years.
Evan Sparks's Aviation Policy Blog 
Russia is itself a “state sponsor of terrorism”, as is the USA.
Iran does not need to “drop” it’s nuclear program, it is perfectly entitled to one for peaceful civil use under the terms of the Nuclear Non-Proliferation Treaty. And considering that the International Atomic Energy Agency has just given Iran a clean bill of health over it’s nuclear program, and accepts its purely peaceful purposes, why on earth should Iran be the object of punitave sanctions?