Russia has voted for tougher U.N. sanctions on Iran and has frozen a deal to send anti-aircraft missiles to that country.
The conventional wisdom is that Russia's economic interests in Iran have led Moscow to be a strong supporter of that country, opposing any tough United Nations sanctions against Tehran over its alleged nuclear weapons program.
But many experts, including John Parker with the National Defense University [expressing his personal views] say relations between Russia and Iran have been worsening.
"They are probably at their lowest point since 1997 when both sides cooperated in bringing the Tajik civil war to a close," he said. "Right now, trade does not amount to that much, a fact that a lot of people don't realize. Russian-Iranian trade is, at its high point, around $3.5 billion a year. And this is not really much more than Russia's trade with Israel, whose population is about a tenth the size of Iran. Iran does a lot more trading with Turkey, for example, and even more trading with China. So economic relations are not much."
Analysts, such as Robert Legvold with Columbia University, say over the past few years, Russian officials have become convinced that Iran may well be enriching uranium with the goal of at least creating the option of developing nuclear weapons.
"They are somewhat less alarmed over the urgency or the imminence of that than the United States - but they have now agreed with the Europeans and the Americans that the Iranians are not acting in good faith in order to demonstrate a commitment to peaceful and domestic use of nuclear fuel, whatever may be the alternative motives that drive them. And therefore the Russians are concerned about Iran and they certainly would not like to see a nuclear Iran - I think there's no question on that score," he said.
To show its displeasure with Iran, experts say Moscow voted in favor of a U.N. Security Council resolution imposing new, tougher sanctions on Tehran - although the text was apparently watered down by Russia and China.
Gaukhar Mukhatzhanova, with Monterey's Center for Nonproliferation Studies [California], says Russian officials have other reasons for agreeing to sanctions on Iran.
"They want also to make sure that the United States and Israel do not feel cornered into taking military action. I think that's Russia's primary interest right now - to on the one hand deliver a message to Iran that they will not support them unequivocally, and on the other hand not allow the military action to go forward," said Mukhatzhnova.
As another example of worsening relations between Tehran and Moscow, experts point to Russia's decision to freeze the delivery to Iran of S-300 anti-aircraft missiles - a deal dating back to 2007.
As for the Bushehr nuclear power plant in southwestern Iran, Russian officials say it will begin operating in a few months [August or September].
David Kramer, a former senior State Department official in the George W. Bush administration, says Moscow also announced that Bushehr will operate as a Russian-Iranian joint venture.
"That was an indication that Russia was not backing off on Bushehr - though let's also remember that the timeline on Bushehr has repeatedly been delayed. And so one can't rule out the possibility that once again, the timetable is going to slip," he said.
Gaukhar Mukhatzhanova says based on recent Russian actions, the Iranians must feel betrayed by Moscow. "Yes, I'm pretty sure they feel that way. But Iran never trusted Russia all that much," he said. "Iran never trusted anybody all that much. And so they do act very betrayed. But I believe that a good proportion of politicians in Iran never truly relied on Russia."
Analysts say given the current poor state of relations between Iran and Russia, Moscow's influence on Tehran is very limited when it comes to curtailing its nuclear weapons aspirations.
"It's a misconception to assume that the Russians have any more leverage than anyone else beginning with the United States over Iran and its nuclear program," said Robert Legvold from Columbia University. "I don't think the Russians have any kind of leverage that would at least independently, that would affect Iran's behavior."
"If Iran begins at some point - and I doubt they will - but if at some point they begin responding to the pressure of the international community, the fact that Russia helps to make it more intact or more complete, may be of some significance. But independent Russian influence, I think is nonexistent on this score - at least not from a decisive point of view," he added.
Analysts say it is difficult to see what kind of pressure can be exerted on Iran to force it to curtail its nuclear weapons program. They say international sanctions can only go so far - and there is still the problem that there is no international mechanism to enforce them.