With the next round of talks between the P5+1 (the five permanent UN Security Council members plus Germany) and Iran scheduled in Vienna on April 7, Russian Deputy Foreign Minister Sergey Ryabkov’s statement that Moscow could take “retaliatory measures” in the negotiations looms large. But just how serious is the threat?

Broadly speaking, Moscow has three instruments of leverage over the Iran negotiations: its UN Security Council veto, its role in the P5+1 process and the Russia-Iran relationship. Russia’s veto looks like the least important of these, as Security Council action is unlikely before the six-month window for negotiations ends in July. At that point, either there will be a deal — which could be costly for Moscow to veto if Tehran is on board — or there won’t. If there is no deal, Russia probably would not have supported (or abstained from voting on) new UN pressure anyway. So no change.

Within the P5+1 process, Moscow can turn a six-nation consensus negotiating position into a five-nation consensus with one outlier. This could complicate (and slow) the diplomatic process but ultimately could not prevent Iran and the others from reaching an agreement if they were able to establish mutually satisfactory terms. China has tacitly accepted Moscow’s annexation of Crimea but has not endorsed it — and consequently seems unlikely to get involved in any effort to obstruct progress on Iran. A larger question is how Crimea will affect US and European attitudes toward the Russia-Iran nuclear relationship. Ideas to involve Moscow in Iran’s fuel cycle seem increasingly implausible politically.

The Russia-Iran relationship is complex and ambiguous. Leaders in Moscow and Tehran appear quite pragmatic — including toward one another, which contributes to mutual suspicions. At the same time, each capital is rife with competing perspectives and interest groups in and out of government, all with their own angles. Understanding who is using whom within and between the two at any given time is not easy.