Good analysis from Douglas Birch of the Associated Press:
So Moscow has walked a tightrope: joining Iran in scolding the West for its alleged imperial ambitions and blocking sanctions on the one hand, while warning Tehran it will not tolerate a nuclear-armed Iran on the other.
Russia has agreed to sell Tehran sophisticated missile defense technology, but has so far declined to deliver those weapons — without giving up the right at some point to do so.
By holding out the hope of sanctions to the U.S., Russia has won a lot of good will in Washington.
By keeping alive the possibility of missile sales and continuing opposition to sanctions, it insures it has friends in Tehran.
By delivering on neither, Russia has irked both would-be allies. But so far it has preserved its influence in a region where, otherwise, it might have little. Or none.