A few weeks, it seems, can make all the difference. For years, Russia has served as Iran's strategic partner and as a key enabler of the Islamic Republic's nuclear ambitions.
Now, however, encouraging signs suggest that relations between Moscow and Tehran are on the rocks.
Since February, Russian and Iranian officials have been locked in an escalating dispute over the centrepiece of their bilateral strategic co-operation: the nuclear plant in the southern Iranian city of Bushehr.
Russian officials have accused Iran of falling behind in its payments of the USD25 million to USD30 million monthly bill for construction of the facility and have already pushed back the launch date for the project - originally slated to begin operations in September 2007.
They have also warned that continued deadlock could have serious implications."We cannot wait longer for a decision by the Iranian side," Vladimir Pavlov of Atomstroyexport, Russia's main nuclear contractor, has said. "Delays in restarting the financing will bring irreversible consequences."
Russia's anger is understandable. Since it was launched in the late 1990s, the USD800 million reactor project has become the focal point of Russo-Iranian nuclear ties. But Bushehr is something of a red herring; its high-profile nature and its hefty price tag make it less than optimal for the real purpose behind the regime's efforts - the development of a strategic nuclear arsenal.
Still, over the past few years, the high price of oil - and the lack of a co-ordinated international response to Iran's nuclear ambitions - has meant that Tehran could foot the bill for Bushehr easily.
Times are now getting leaner; international measures, however halting, have already begun exacting a cost from the Iranian regime, forcing it to begin to deplete its oil revenue 'slush fund' and to contemplate drastic measures such as gasoline rationing.
Against this backdrop, the Iranian leadership appears to have decided to scale back its participation in the Bushehr project, harming Russia's bottom line in the process.
Another calculus could be at play as well. In recent months, Russian President Vladimir Putin has revived the notion of a Moscow-dominated natural gas counterpart to OPEC.
A February session of Russia's legislature, the State Duma, was reportedly devoted to the feasibility of such a cartel and sources say that such a bloc - potentially encompassing as many as 16 countries, including the world's largest natural gas producers (Russia, Iran, Qatar, Venezuela and Algeria) - is currently being set up at the direct urging of the Kremlin.
In support of this effort, Putin recently paid a high-profile state visit to the Gulf and presided over the sixth meeting of the Gas Exporting Countries Forum in Doha, Qatar, where his ideas for a new energy bloc were actively discussed by those present.
However, there is a price for this plan. For the countries of the Gulf, deeply apprehensive of Iran's runaway nuclear effort, the Islamic Republic's strategic co-operation with the Kremlin appears to have become a source of concern and was probably a major part of the behind-the-scenes diplomatic horse-trading. In other words, Russia's tougher tone vis-a-vis Iran may be at least partly the result of pressure from Moscow's emerging energy partners in the Middle East.á
Whatever the reasons, the Kremlin's very public falling out with the Iranian regime appears to have substantially shaken up the policy status quo in Moscow.
There has always been a strong minority opinion in Moscow (articulated by the likes of former Duma Deputy Alexei Arbatov) that co-operation with Iran has the potential to become a double-edged sword.
These arguments, long suppressed by official policy, are now rising to the fore. As prominent Russian military analyst Pavel Felgenhauer put it recently: "[If] the Islamist regime acquires nuclear weapons, anything could happen."
Kremlin insiders seem to agree. Yevgeny Velikhov, secretary of the Russian Federation's influential Public Chamber and a close confidant of Russian President Vladimir Putin, has joined the growing chorus of voices publicly warning about the dangers posed by Iran's nuclear ambitions.
"It is important that Iran does not get nuclear weapons," Velikhov recently told reporters in Moscow in a statement that almost certainly reflects the official Kremlin view on the subject. "If Iran gets nuclear weapons, it will be very negative for the security of the whole world."
The question, as always, is whether the US and its allies are properly positioned to exploit these fissures in the Russo-Iranian entente. On that score, the jury is still very much out.