Russia is not currently implementing its planned sale of sophisticated S-300 air defense systems to Iran, a top official with the state office for arms sales told Interfax. "Nothing is happening. Supplies are not taking place," said Alexander Fomin, deputy head of the Federal Service for Arms Cooperation, at an arms fair in Rio de Janeiro.
Russia's plans to provide the systems to Iran have attracted criticism from the United States and Israel, neither of which have ruled out attacks on Iran's controversial atomic facilities. The comment came after an unnamed official at the same agency said last month delivery of the defense systems, intended to shield key areas from attack, would depend on the "developing international situation and the decision of the country's leaders."
The Ynet article goes on to suggest Russia’s change of heart has more to do with international pressure being leveraged against the sale and the new, warmer friendlier ties with the US – which I find no evidence of. If anything, I would say the Russians have been much more dismissive of the Obama Administration. I am betting it has more to do with a Lieberman/Israeli connection.