Currently Iran already operates the S-300 anti-air defense system, but just ahead of the major UN weapons embargo set to expire this month, which the US contests, Russia has once again strongly suggested that it's poised to transfer its more advanced S-400 system to Iran.
The latest comments on the issue were made Saturday by Russia's ambassador to Tehran Dzhagaryan who told an Iranian newspaper Saturday it would be "no problem" for Moscow, in effect signaling a green light for such a deal.
"As you know, S-300s have already been delivered. Russia has no problem delivering S-400s to Iran. This was never a problem from the very beginning," the ambassador said.