It is funny that Russia is giving us a warning about doing something that they agree must be stopped. If Russia really wanted to stop Iran, they would be showing a united front with us.
I'm wondering whether the actual story is that they know Iran has nukes now, they are intimidated by it and are hoping to stay on Iran's good side (such as it is) until they feel they have developed sufficient deterrent powers. I don't think Iran is rationally deterrable, in any case, but that might account for the stranged mixed messages issuing from Moscow.