The once-cozy relationship between Russia and Iran has undergone a striking shift in recent months, as Moscow has grown increasingly critical of Tehran's defiant pursuit of nuclear capabilities. The Kremlin has even warned that it could support sanctions against Iran in the UN Security Council -- something it resisted for years.
In turn, top Iranian officials have accused Russia of succumbing to US and Israeli pressure and complained that Moscow is dragging its feet on fulfilling a contract to supply Iran with advanced S-300 anti-aircraft missiles. In addition, Iran is voicing frustration at delays in the launch of its first nuclear power plant, which Russia's state-owned atomic energy company, Rosatom, is building in the southern Iranian city of Bushehr.
But analysts say the current chill in Russian-Iranian relations is likely to be temporary, since Moscow and Tehran have a shared interest in bilateral trade and in defying the West. Moreover, the Kremlin cannot afford to alienate Iranian leaders because of the potential threat that Iran poses in Russia's post-Soviet backyard.
"The relationship right now is fairly tense," said Fyodor Lukyanov, editor of the journal Russia in Global Affairs. "But normal relations with Iran are very necessary for Russia because Iran's influence on adjacent territories, such as the Caspian Sea region and Central Asia, is undoubtedly very important."
The relationship between Russia and Iran, long characterized by mutual suspicion and regional rivalry, appeared to blossom during the presidency of Vladimir Putin, just as Moscow's ties with Washington were rapidly deteriorating. In 2007, Putin became the first Kremlin chief to visit Tehran since Joseph Stalin -- a pointed rebuke to former US President George W. Bush's efforts to isolate the Islamic Republic.
In September of 2009, however, amid growing international tension over Iran's nuclear program, Russian President Dmitry Medvedev dropped the first hint that Moscow might use its status as a permanent, veto-holding member of the UN Security Council to back a new round of sanctions against Iran. The same month, Moscow reacted angrily to the revelation that Iran had built a secret uranium enrichment plant near its holy city of Qom.
Moscow was further frustrated when Tehran backed out of a deal brokered by the International Atomic Energy Agency that had been hailed as a way out of the nuclear standoff. The proposed IAEA plan, under which Iran would ship its low-enriched uranium to Russia and France for further processing, had been seen by Moscow as "very favorable and positive," Lukyanov said.
In February, Iran seemed to cross a red line for the Kremlin by declaring that it had begun enriching uranium to a level of 20 percent, a step that puts Tehran significantly closer to having weapons-grade fissile material. Following Iran's announcement, the powerful head of Russia's National Security Council, Nikolai Patrushev, said that doubts about the peaceful intention of Iran's nuclear program were "fairly well-grounded." Those comments marked the first time Moscow had joined the West in suggesting that Tehran was seeking to build an atomic bomb. Iran insists that its nuclear program is for civilian purposes only.
"Russia has one strategic goal that fully coincides with those of America and Europe: Russia very much does not want a new nuclear-armed state on its borders," said Alexander Konovalov, head of the Institute of Strategic Assessments in Moscow. "It is a much more immediate problem for us than for the United States."
The Kremlin faces a delicate balancing act as it tries to slow down Tehran's nuclear drive while maintaining a workable relationship with Iran, which lies less than 200 kilometers from Russia's southern border. Notably, Moscow has refused to endorse Western proposals for "crippling sanctions" such as a ban on gasoline exports to Iran.
Diplomats from the five permanent Security Council members - the United States, Britain, France, China and Russia - and Germany were expected to meet at UN headquarters in New York on April 14 to discuss possible new sanctions against Iran.
"Moscow realizes that international pressure, no matter how strong, may fail to prevent Iran from acquiring nuclear weapons, while it is quite probable that Russia's participation in this pressure will antagonize Iran. As a result, Russia may end up with a neighbor that is both unhappy with Moscow and has nuclear arms," said Simon Saradzhyan, a researcher at Harvard University's Belfer Center focusing on Russian security issues.
An alienated Iran could potentially stir up trouble for Moscow by supporting the Islamist insurgency in Russia's North Caucasus, opposing Russian interests in the Caspian region and Central Asia -- including in Persian-speaking Tajikistan -- and helping Armenia diversify away from its dependence on Russian energy, Saradzhyan said.
But the chill in Russian-Iranian ties is unlikely to lead to such a stark rupture, analysts say. Not only does Moscow have hundreds of millions of dollars' worth of arms contracts with Tehran that it is reluctant to sacrifice, it also enjoys powerful leverage with the West as long as it continues to be a key player in the nuclear standoff -- a privileged role that Russia would lose if it aligns itself fully with the United States.
"Full-fledged sanctions will not get Russia's support," said Alexei Malashenko, a political analyst at the Carnegie Moscow Center. "Russia needs Iran in order to demonstrate the independence of its foreign policy from that of the United States and the West."
Moreover, any new UN Security Council sanctions would need support from China, which has so far been reluctant to give its blessing. Combined with Moscow's ambivalence, that means any new sanctions will probably have little impact on countries like Azerbaijan and Turkmenistan that have important trade links with Iran.
Alexander Osipovich is a Moscow-based writer who specializes in regional affairs.