Russia built for Iran its first nuclear power plant, then refused to sell to Tehran the anti-aircraft missiles to defend it.
A high-ranking Russian told reporters in Moscow on Tuesday that it ?remains unproven? that there is a military component to Iran?s nuclear program.
On the other hand, he added, Tehran?s decision to enrich uranium violates international resolutions designed to keep Iran from acquiring a nuclear bomb.
As tensions rise between the West and Iran over Iran?s nuclear program, Russia is trying to play a highwire balancing act.
Pyotr Topychkanov studies nuclear non-proliferation for Carnegie Moscow Center. ?Russia does not want Iran with a nuclear weapon,? said Topychkanov.
He said a nuclear-armed Iran would start a regional arms race, starting with the Sunni Muslim Gulf monarchies that ship their oil to the outside world through the Strait of Hormuz. Iran, a Shi'ite Muslim nation, has threatened to close the strait, if pushed too hard on the nuclear issue.
Closer to home, the Kremlin worries that if Iran gets a nuclear bomb, Russia?s historic southern rival, Turkey, will race to get its own nuclear weapon.
Evgeny Satanovsky runs the Near East Institute in Moscow. He speaks of Russia?s new worry about Turkey and its increasingly aggressive prime minister, Recep Tayyip Erdogan.
?We have in Turkey the new Ottoman Empire. Recep Tayyip Erdogan is a man with a very dangerous ambition, and he looks at himself a new Ottoman Sultan,? he said.
Satanovsky says good relations with Turkey and Iran are essential for keeping the peace in Russia?s Muslim south. A century ago, the inhabitants of Russia?s Southern Caucasus were called ?mountain Turks.? Today, they still resent rule by Moscow. In Dagestan, a low-level insurgency take lives almost daily.
Satanovsky worries that an angry Iran would strike back at Moscow by bankrolling Muslim extremist groups in Russia?s Caucasus.
?Don?t touch them too aggressively, because they can destabilize the Northern Caucasus, the Russian Dagestan or some other territories for a few months," he said.
Nikolai Patrushev, head of Russia?s Security Council, told Interfax last week that Washington is plotting regime change in Iran.
Satanovsky believes that a civil war in Iran would force up to three million people to take refuge in Russia and Azerbaijan, a former Soviet republic.
Historically, when Russia?s power and population was growing, the Kremlin repeatedly sent troops into Northern Iran. From the 1880s to the end of World War II, northern Iran was either occupied by Russian troops or considered a zone of Russian control.
Today, Russia?s population is aging and shrinking. Its military might is a shadow of its Soviet strength.
Topychanov at Carnegie says Russia is less a player and more a bystander in events to its south. ?After the collapse of the Soviet Union, Russia does not have the resources to play an active role even in this region,? he said.
After losing the czarist and Soviet ability to project power, the Kremlin now opposes interference in the internal affairs of other countries.
As the world watches growing tensions in the Strait of Hormuz, Russia?s battles in connection with Iran are expected - this time - to be entirely diplomatic.