Russian President Vladimir Putin is trying to send someone a message with his April 13 decree authorizing the delivery of S-300 surface-to-air missiles to Iran. But who?

The most striking aspect of the decree is its timing. Exactly a week before the Kremlin announced the decision, I argued that the S-300 sale — contracted in 2007 and suspended by former President Dmitry Medvedev by decree in 2010 — was likely to follow a final agreement on Iran’s nuclear program, under negotiation with a June deadline. In brief, I wrote, since Russia viewed Medvedev’s steps to halt the sale as a voluntary gesture to the United States, Israel and others trying to press Tehran to negotiate, there would be no reason for Moscow to continue to withhold the missiles after a final deal.

Yet, publicly announcing this intent in advance is another matter entirely. Putin’s formal presidential action — while negotiations are still underway — cannot but complicate efforts to reach a final agreement, most notably by strengthening the arguments of skeptics in the US Congress. They will in turn put greater political pressure on the Obama administration for tougher terms. In fact, by focusing on the Russia-Iran arms relationship when there is already apparent disagreement between the United States, Iran and other parties to the talks over when the UN Security Council should lift sanctions, the Kremlin’s move could create a situation in which Washington takes a harder line on conventional arms restrictions than Iran is prepared to accept.

What makes the decree’s timing most remarkable is that it will probably take quite some time for Moscow and Tehran to reach an understanding on the S-300s and to arrange the delivery. Nikolai Patrushev, a close Putin associate who leads Russia’s Federal Security Service, said that he believes the manufacturer “will need at least six months to complete this work.” If this is true, why not make a quiet arrangement with Iran, start getting the missiles ready and then announce the deal and the decree after the end of June, which is only 10 weeks away? This is the critical question.