It’s always been a puzzle to me (other than the Russians need for cash,) but this is the most sensible (and about the only) explanation I’ve seen yet:
While Russia had, until recently, vetoed UN Security Council resolutions against the Iranian nuclear program, Medvedev suddenly hardened his rhetoric, mentioning sanctions as a possible course of action. Either way, it is quite clear that Russia, which borders Iran on the Caspian Sea, does not fear the emergence of its new nuclear neighbour and is even actively aiding the construction of the nuclear station in Iran. Why? The reasons are manifold.
Middle Eastern politics are never simple. Throwing the Russians into the mix only makes it worse.
The leitmotif of this whole business is counteracting the U.S. But if things keep going the way they are, they’ll be looking for someone else to counteract in the near future.