Tehran and Moscow, facing similar political and economic pressures from the West, have developed strong ties since the Islamic Revolution. More recently, as relations between the US and Moscow have soured, the links have only intensified. But for Tehran, closer ties to Moscow are not so much a choice as the only viable option — and in the run-up to the deadline for a comprehensive international deal on the Iranian nuclear programme, Moscow’s influence looms dangerously large. Decisions made in the next few days by the US, China, France, the UK and Russia, plus Germany (the “P5+1”) and Iran, will determine whether that remains the case.

In fact, Iran’s interests today, as in the past, overlap more with those of the US than either side is willing to admit. It is true that since the 1979 revolution turned Iran from Washington’s ally to one of its most vocal opponents, Moscow has stepped into the void. The two countries co-operate on strategic matters including energy, technology, aerospace, defence and trade.

Moscow provides military equipment Iran cannot procure from the West, and also assists in civilian arenas. It is Iran’s sole nuclear partner, supplying technology and fuel. It stepped in when the West left the Bushehr nuclear power plant unfinished after the revolution. The two countries have recently concluded a deal to construct two further plants. US and Iranian interests are aligned in much of the Middle East. Yet in a number of areas they are unwilling to co-operate. As Tehran engages with the world powers on its nuclear dossier, domestic politics allow little scope also to co-operate openly with the West on regional security issues. For Washington, domestic constituencies such as a Republican-controlled Congress — and regional allies including Israel and Saudi Arabia — are expressing concern at the idea of the US striking a “bad deal” in order to tackle the issue of Daesh (Islamic State of Iraq and the Levant) in co-operation with Iran.

Meanwhile, Tehran and Moscow are creating an axis of their own, and co-operating to push Daesh back. They have begun co-operating in Iraq. They are also on the same team — that of President Bashar Al Assad — on the Syrian civil war. They pledged at the 2014 Caspian Sea Summit not to let foreign powers intervene in the region, limiting Nato’s ability to deploy forces. Subsequently they conducted joint military drills in the area. To overcome sanctions, they are developing a plan to replace the US dollar with their national currencies in bilateral trade.

Iran is not forging closer ties with Russia because it believes Moscow is a viable, trustworthy partner, however. During the pro-reform protests that followed the disputed 2009 presidential election, the revolutionary slogan “death to America” gave way to “death to Russia”, reflecting frustration at substandard technology believed to be endangering lives. Tehran’s insistence on developing indigenous nuclear technology and becoming self-sufficient stems from this. Iranians believe their country can neither meet its needs on the global market nor rely on Russia. This isolation has left Tehran no option but to turn to Moscow. And, as relations between the US and Russia have deteriorated, the state has the scope to become an evermore decisive and divisive factor. Failure to reach a comprehensive deal on Iran’s nuclear programme, and to lay the path for more normal economic and political relations with the world, would propel Tehran into Moscow’s arms. It would foster an even more powerful Russian-Iranian axis. This would be worrying for opponents of a deal on Capitol Hill, most of whom also do not want Russian influence to grow. By blocking the way to a deal, they could facilitate and accelerate what they want to prevent.

— Financial Times

Ariane Tabatabai is an associate with the Harvard Kennedy School’s Belfer Center for Science and International Affairs.