Russia Toughens Stance on Iran - Why?

Reuters: Russia warns Iran over nuclear program

This is a strange move of sorts from Russia. The Kremlin has always been reluctant to impose sanctions on Iran, and have been only more reluctant since the infamous National Intelligence Estimate on Iran’s nuclear capabilities came out at the end of last year. Why the change in the position?

Recent events
Did any recent events provoke Russi into making this move?
Kosovo independence (and Russia’s inability to prevent it)?
• Upcoming Russian elections?
• The recently released IAEA Iran report (which eased some pressure on Iran)?

None of these events seem a likely impetus for Russia’s actions, for mostly obvious reasons:
• Why would Russia want another geopolitical loss after Kosovo?
• Putin is expected to stay in power in elections anyway.
• The IAEA report made Iran look like the good guy.

Another possibility
It is quite possible the White House made a deal with Russia and Putin to move forward with sanctions. The details such a compromise would entail can only be guessed at.

Russia looking to provoke Iran?
Though this is more of a conspiracy theory like idea, it cannot be ruled out. The U.S. and Iran have been engaged in talks for a while now, and could be nearing a deal. By threatening to agree to new sanctions, the former superpower could turn up the heat on Iran, which could aggravate Iran, causing Tehran to cancel any deal it might have worked out with the U.S.

What should the U.S. do?
The U.S. has a fairly easy decision to make, from my point of view. If talks with Iran are producing results, sanctions should be delayed. If talks are going no where, hat tip Moscow and pursue further sanctions.