Iran’s relationship with Russia has been characterised as many things, ranging from a ‘marriage of convenience’ to a ‘long-lasting alliance’. In reality it's a  pragmatic working relationship forged between two countries that  have faced similar political and economic pressures from the West. The increasingly vitriolic exchanges of the past week, however, suggest that both are finding the relationship harder to manage.

As two leading anti-US states with an alternative vision of a world order, Russia and Iran developed ties in multiple sectors. For both countries, working with the other has been a useful counter-balance to US dominance. Economic ties between the two helped each to weather Western-imposed sanctions. In the military sphere, Moscow provided Iran with equipment it couldn’t get from the West and conducted joint-military exercises in the Caspian Sea. Shared foreign policy goals in the Middle East – including keeping Assad in power in Syria and pushing back ISIS in Iraq – led to intelligence cooperation. Russia is also Iran’s sole nuclear provider, committed to completing Iran’s Bushehr power plant and supplying fuel for its first 10 years of operation. A number of other plants are planned.

But now it seems leadership in each country is weary of the other.

The Russians are not perceived well in Tehran. In the nuclear field for example, Iran has repeatedly accused the Russians of being unreliable. Moscow also firmly supported efforts to prevent a nuclear-armed Iran, despite its feelings towards the West. In the military sphere, Moscow dragged its feet in the sale and delivery of the S300 air defence system: signing a contract in 2007 but not making its first delivery until April this year. Economically, and particularly in the energy sphere, the two countries are competing for a bigger slice of a shrinking pie. Both want to increase oil exports and Iran has long-term plans to boost natural gas exports to Europe in particular: traditionally, Russia’s market. Iran’s negative feelings toward Russia were part of the reason why it pursued the nuclear deal to begin with: it needed other partners.

But it was the conflict in Syria that simultaneously brought Russia and Iran closer together and highlighted the differences between them. Their shared goal of preserving the Assad regime saw them work more closely together; coordination and dialogue increased. But each sides perceived the relationship differently.

Tehran thought it had the upper hand; that in Syria at least, it was dictating the terms of the cooperation. After all, it was Iranian men involved in the fight on the ground and gathering intelligence. From Iran’s perspective: Russia ‘only’ provided air cover for their fight. For its part. Moscow  felt it was useful to cooperate with Iran because it didn’t want to lose the privileged position it had pre-nuclear deal. But it firmly (and perhaps more accurately) saw its role as that of a bigger, more powerful and more capable friend coming to the aid of Iran, a regional powerhouse that needed help in its own backyard.

When it became apparent that Tehran wasn’t in charge, the Iranians were taken aback. They were surprised when Russia did not inform them that it had agreed to a ceasefire with the US, when Russia temporarily halted airstrikes against the al-Nusra Front in May, and again in July when Secretary Kerry and Foreign Minister Lavrov announced an agreement – the contents of which were not shared – to cooperate on respecting the ceasefire.

This trend was only reinforced when Russia announced that Iran had allowed it to use the Hamedan base for its bombers on the way to Syria. Given the Iranian constitution explicitly prohibits the establishment of a foreign military presence on its soil, some in Iran, including parliament, were less than impressed. Defense Minister Brigadier General Hossein Dehqan criticised Moscow for 'showing-off' when it leaked the news, and said that the decision to sign a treaty for strategic military cooperation with Russia was made by the 'system', and was none of the parliament's business. Various officials have since downplayed the event; the Foreign Ministry announced activities were halted, while the speaker of parliament Ali Larijani stated Russians were just refuelling their bombers.

Why, given Iran’s frustrations with Russia, did Tehran give Russia permission to use its base? Likely because it was counter-balancing recent Gulf Arab efforts to court Moscow into their camp and because, ultimately, Tehran knows it needs Moscow in Syria. But the very public spat following the leak demonstrates this is not an easy relationship.