• Russia has rejected an Iranian request to buy S-400 missile defense systems, concerned that the sale would stoke more tension in the Middle East.
• The request was rebuffed by President Vladimir Putin on condition of anonymity because they’re not authorized to discuss the matter.
• Iranian Foreign Minister Mohammad Javad Zarif visited Moscow May 7. Russia’s Foreign Ministry didn’t reply to a request for comment, and Iranian officials couldn’t be reached for a response.

BACKGROUND:

• The US recently imposed more anti-Iranian sanctions and sent an aircraft carrier and bombers to the Gulf over what it described as a threat of attack from Iran on its forces and allies.
• Russia’s reaction to Iran’s request reflects the delicate balance of power in the Persian Gulf, where a showdown is brewing between the Islamic Republic on one hand, and the U.S. and its Gulf Arab allies on the other.
• President Donald Trump agreed to send more U.S. troops to the region after the U.S. blamed Iran for attacks on Saudi oil installations as well as four ships.