One of the many unanswered questions surrounding the so-called framework agreement on Iran’s nuclear program is whether and how it will limit Russia’s arms trade with Iran, including Moscow’s long-standing interest in selling advanced surface-to-air missiles. In fact, managing the Russian-Iranian military relationship may become increasingly difficult if the negotiating parties reach a final agreement by their self-imposed June deadline.

For the United States and Israel, one of the most controversial Russian-Iranian transactions was the 2007 contract to sell S-300 surface-to-air missiles, which officials in both countries considered a potentially serious obstacle to any military action targeting Iranian nuclear sites. In September 2010, former Russian President Dmitry Medvedev issued a decree blocking the S-300 sale, as well as other conventional arms sales to Iran. Medvedev’s action followed UN Security Council Resolution 1929, approved in June 2010, banning the sale to Iran of “battle tanks, armored combat vehicles, large caliber artillery systems, combat aircraft, attack helicopters, warships, missiles or missile systems.”

Because Iran had already paid for the S-300s under an $800 million agreement, Tehran sued Russia’s state arms supplier for nondelivery and demanded $4 billion. In January, official Russian media reported that the two sides had settled their differences after Moscow agreed to provide older Tor surface-to-air missiles with an unspecified date of delivery. Iran’s state media also reported a settlement, but without providing details. At around the same time, reports emerged also that Russia and Iran were again discussing either the S-300 system or a newer system, the Antey-2500.

The US version of the “parameters” that comprise the Lausanne framework agreement includes the statement “all past UN Security Council resolutions on the Iran nuclear issue will be lifted simultaneous with the completion, by Iran, of nuclear-related actions addressing all key concerns.” The document adds, however, that “important restrictions on conventional arms and ballistic missiles” will be re-established in a new resolution. Meanwhile, the joint statement read by European Union foreign policy chief Federica Mogherini and Iranian Foreign Minister Mohammad Javad Zarif says only that this new UN resolution will “incorporate certain restrictive measures.” Since the Lausanne deal is a general agreement, with precise terms not yet outlined or in some cases agreed to, it is unclear what these differences will mean in practice.