Russian strategic bombers launched from Iran struck rebel positions in Syria on Wednesday, in a second day of attacks that multiply Russian firepower in the Middle East and underscore unprecedented military cooperation between the Islamic Republic and a foreign power.

The Kremlin says the Tu-22M3 bombers attacked targets of the so-called Islamic State (IS) and other factions in Syria that oppose President Bashar al-Assad, an ally of both Moscow and Tehran.

The closer cooperation serves both to target opponents of Mr. Assad – some of them backed by the United States – while also sending a sharp message to the US as fighting over the divided city of Aleppo reaches a critical point after five years of inconclusive civil war.

Iran’s decision to openly allow foreign troops on its soil for the first time since the 1979 Islamic Revolution – and the first Russians since World War II – is testament to its desire to achieve strategic gains and ensure that the high cost of its involvement in the Syrian war, including the loss of more than 400 Revolutionary Guard troops and a number of generals, not be in vain.

For Russia’s part, its decision to use the Shahid Nojeh military airbase in western Iran underscores its calculation that bolstering its nearly year-long overt military intervention – which began dramatically with Russia airstrikes launched from a base in the Syrian coastal town of Latakia – can help tip the battlefield in Assad's favor.

Perhaps just as significantly, the high-profile move allows both nations to ease their isolation, imposed by the US and the West, while spreading their regional influence through the use of hard power.

“It means that keeping Assad in power is very important for Iran, and for Iranian hardliners too, since they are allowing an infidel military on their sacred territory,” says Pavel Felgenhauer, a defense columnist for Novaya Gazeta in Moscow.

“The Iranian and Russian strategic intent in Syria seems much closer than the Russian and American strategic intent in Syria,” says Mr. Felgenhauer, referring to an earlier agreement by the US and Russia to seek a negotiated solution. “I was a bit surprised that the Russian defense ministry so promptly [acknowledged] that we are in Iran…. The Russian military tends to be secretive, so that was a political decision to demonstrate to the world that Russia and Iran are militarily together.”

Since last November, Russia’s strategic bombers have had to fly from an old Soviet airbase at Mozdok in southern Russia. The 650-mile distance to Aleppo from Mozdok is not much shorter from the western Iranian base near Hamedan, as the crow flies. But Russian planes must skirt Turkey, and targets in eastern Syria – and also anywhere in Iraq, should Russia eventually choose to take on IS targets there – are significantly closer from Iran.

Flying out of Iran, therefore, enables Russian jets to carry full payloads of 24 metric tons – more than the maximum for the longer run from Russia, notes Mr. Felgenhauer.

“That is of course significant, because since they are carpet bombing Syria, the more bombs you take, the more land you cover,” he says. “Right now at this pivotal point in the battle for Aleppo, it is very important that Russia has drastically increased bomb-carrying capability, to bring the bombs to the Syrian opposition.”

A top Iranian official said the new arrangement was Syria-specific but also “strategic,” and a “warning to terrorist-supporting countries” – an oblique reference to the US and its allies, which want to see Mr. Assad removed from power.

While Iran- and Russia-led cooperation had already made life “very tough for terrorists,” the new expansion “will continue until they are completely wiped out,” said Ali Shamkhani, the head of Iran’s Supreme National Security Council, on Tuesday.

Top Iranian lawmaker Alaeddin Boroujerdi noted today that Russian planes were only refueling at the base, and that “generally, there is no stationing of Russian forces” in Iran.

Washington called the move “unfortunate” and said it “pushes us farther away” from a nationwide cease-fire and the UN-sponsored political process in Geneva that includes Russia. Earlier this week, Russian defense chief Sergei Shoigu was quoted saying the US and Russia were in “a very active phase” of talks about the surge of fighting in Aleppo, “to start fighting together to bring peace.”

US officials would say only that they are in “close contact” with Russia as they push for a negotiated solution to a war that has ravaged Syria, claimed more than 400,000 lives, and produced nearly 5 million refugees. The US-led air campaign against IS in Syria and Iraq has help reduce territory of the self-declared caliphate by 30 percent, according to the Pentagon.

But while Russian airstrikes have hit IS jihadists, US officials say that many more since last year have struck anti-Assad forces backed openly or clandestinely by the US and its allies. President Vladimir Putin ordered a Russian withdrawal last March, and troops were filmed returning home. But there has been little slowdown since, and on Tuesday Russia’s defense ministry said it “eliminated” five weapons depots in the first day of new strikes.

A delicate issue

The Russian military presence is sensitive in Iran, where revolutionary ideology since 1979 opposed both US and Soviet influence during the cold war, and categorically, in rhetoric at least, rejects foreign meddling.

Ali Larijani, Iran’s speaker of parliament, reminded lawmakers on Wednesday that it was “forbidden” by the Constitution to create a foreign military base, and that Iran had not “given the base over to Russia in military terms.”

The Iran-Russia cooperation results from “the crisis of terrorism that has been created by some destructive countries in the region and America, therefore we think that Russia has found the right treatment for the region,” said Mr. Larijani. Top Iranian officials often accuse the US of creating and backing IS and other jihadists fighting Assad, claiming it is a bid to undermine their own Iran-led axis of resistance against US and Israeli influence in the region.

Indeed, the Iran-Russia cooperation is temporary, defined by mutual recognition of the threat of IS, and “is not a coalition against a third-party state [such as] the US, Saudi Arabia, or Turkey,” says Kayhan Barzegar, director of the Institute for Middle East Strategic Studies in Tehran.

It is “true that taking the lead in battling and destroying Daesh [IS] in Syria and Iraq will have broader geopolitical consequences for rival states, but Moscow and Tehran have never wanted to exclude other actors from the Syrian scene,” says Mr. Barzegar. “Their military cooperation is only aimed at accelerating the political solution and not winning the war in a zero sum manner. Therefore, Washington and its allies, if determined to defeat IS, should not feel concerned [about] possible long-term strategic consequences.”

Ups and downs

Russia-Iran relations have varied, often pragmatically but sometimes capriciously, according to broader agendas and with an eye to the US. Russia built Iran’s only nuclear power plant at Bushehr, but finished it years late and with frequent disputes over payments that at times seemed to emerge only when Russia was trying to cozy up to the US.

In the 1990s, Iran refrained from backing Islamist Chechen rebels in their fight against Moscow in the 1990s, even as it supported similar militias elsewhere. Yet Russia repeatedly voted alongside the US to impose UN Security Council sanctions on Iran over its nuclear program.

And earlier this year – as sanctions over Iran’s nuclear program eased as part of a July 2015 accord with world powers – Russia agreed to sell Iran its S-300 anti-missile system, among many other arms sales. Iranian media reports that “substantial” parts of the S-300, which is to defend Iran’s nuclear sites, have already been delivered.

But while both sides have downplayed any greater regional ambitions, others see a larger strategy at play.

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“There could be more, and the possibility of spreading the Russian air campaign to Iraq," says Felgenhauer. “The thing is not about Syria per se. Syria is important, but there is more: Russia wants to spread its influence over the entire region, have bases all over, push the Americans out and become the dominant power in the region."

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