As Bar'el points out, there ain't much point in UNILATERAL sanctions if you don't hold a monopoly on those goods and services. The USA and EU can impose its "additional sanctions" as much as it likes, and that ain't worth Jack Shit if (a) China isn't one of the States of The Union, and (b) the EU keeps knocking back Turkey's membership application, because while (a) and (b) applies then Iran can simply buy from China and Turkey. And if neither of them offer a good enough price then Iran can simply go to the Russkies and ask them for a quote. UN-mandated sanctions make sense. Unilateral sanctions do not.
Islamic State blows up tower tombs in Syria's Palmyra (Reuters)
from the article: Neighbors / Iran above Islam