Alan Philps has a very good article today in the National:
A clear cause for the cooling of relations between Moscow and Tehran is the Iranian rejection of a Russian-supported proposal under which Iran would send low-enriched uranium to Russia and France for enrichment. This proposal had nothing to do with nuclear weapons: the nuclear material was for use in a research reactor for medical purposes. The Kremlin has not taken this rebuff lightly.
A lot of effort and Russian prestige went into putting together this proposal.
There are objective reasons for the Russians to be angry with Iran, and to ditch their previous reticence about sanctions. These factors coincide with a subtle change in the balance of power inside Russia between Mr Putin and Mr Medvedev. Mr Putin hand-picked his successor, having eliminated all other rivals, and it was generally assumed that Mr Medvedev would be keeping the seat warm for him to return to the presidency in 2012. (…)
Ultimately, I see the rebalancing of forces in Russia as subtle rather than game-changing, and likely to be played out over a long period.
As for Iran, it is well to remember that Russian foreign policy is motivated by fear of losing influence, and being relegated to the third rank of states. With Iran, it is in a position of great influence and is quite comfortable dealing with this. When Iran treated Russia’s proposal with disrespect, the mullahs should have expected a combative response.