After world powers reached a preliminary agreement with Iran in April that is meant to prevent it from developing nuclear weapons, Russia quickly unblocked the delivery of sophisticated S-300 missile defense systems to the country.

The weapons system could reduce the scope of Israeli and possibly Saudi attacks on Iranian nuclear facilities. Both states have expressed discontent with the nuclear talks which they feel do not go far enough to stop Iran’s program.

Russia originally suspended the delivery of the S-300s in 2010 in support of an international effort to force Iran to the negotiating table, despite it having already paid $167 out of $800 million for the systems.

In January, a Russian military official was quoted saying Iran could possibly get the even more advanced S-400 air defense system, suggesting that the decision to supply the S-300s was made before significant progress was made in the nuclear talks in Lausanne, Switzerland three months later.

Russia’s decision to arm Iran is informed by at least two factors.

First is that it sees a China-Iran-Russia axis as a counterweight to the American-dominated NATO alliance. The need for such a counterweight has increased since the West imposed financial sanctions on Russia after it invaded and annexed the Crimean Peninsula for Ukraine last year.

The sanctions are the second reason for selling Iran the S-300s. They have conspired with low oil prices to push Russia’s economy into recession. Defense sales provide much-needed revenue. Iran is planning to spend up to $40 billion on modernizing its armed forces. Russia could find a lucrative new market in the Middle East. Russian defense minister Sergei Shoigu has already spoken hopefully of a “long-term and multifaceted” military relationship with the Islamic state.

The implications of the S-300 sale are profound. It raises the risk of an arms race in West Asia where Russia and the United States back opposing sides. Israeli, Saudi Arabia and the other Arab Gulf states would see the lifting of sanctions as well as further Russian arms sales to Iran as a reason for bolstering their own defenses.

Moreover, the sale is damaging to Israeli-Russian relations. It was reported last year that Israel had plans to sell unmanned aerial vehicles to Ukraine, the former Soviet satellite state Russia invaded last year. Israel stepped back from arming Ukraine at the time, possibly to dissuade Russia from supplying the S-300s to Iran. Now that Russia has gone ahead with the Iran deal, Israel may no longer feel restrained to provide weapons to the Ukrainians.