Russia has defended the sale of sophisticated missiles to Iran, saying the deal will not upset the balance of power in the Middle East. The United States and Israel have both strongly criticized the sale.
Russian Defense Minister Sergei Ivanov has confirmed that Russia will sell Iran tactical surface-to-air missile systems.
But he describes these as "purely defensive" in nature, and that Iran's acquisition of them "in no way" upsets the balance of forces in the Middle East.
Russian media have reported that 29 mobile air defense systems are part of a deal worth an estimated $700 million.
When reports of the sale first surfaced, an Iranian security official expressed surprise there should be any concern.
But Israel has strongly denounced the move, with a foreign ministry spokesman saying it "serves only the interests of the most negative elements in the region."
The United States has also criticized the deal.
Alexei Malashenko is with the Carnegie Center in Moscow. He says that while the weapons sale might be surprising, it is also predictable politically.
"Russia by all means wants to keep its special relationship with Iran," said Alexei Malashenko. "It is very important for Russia, for Moscow to prove to anybody that Russia is able to pursue its independent foreign policy in this area, in particular in this region."
He adds that the new weapons will help Iran present itself as more of a power in the Middle East, and even take a stronger position in its dealings with the United States. This would include the ongoing dispute over Tehran's alleged nuclear-weapons program.
Russian engineers have been building a nuclear power plant in Iran, which both countries insist is only for peaceful purposes. And Moscow strongly opposes any possible referral of the Iranian nuclear issue to the U.N. Security Council.