Iran's Foreign Ministry officials announced that Russia delivered the first part of the S-300 surface-to-air missile defense system. The S-300 surface-to-air system was first deployed at the height of the Cold War in 1979.The S-300 surface-to-air system was first deployed at the height of the Cold War in 1979. In its updated form it is one of the most advanced systems of its kind and, according to British security think tank RUSI, can engage multiple aircraft and ballistic missiles around 150 km (90 miles) away.The contract was revived last year after Iran and six leading world powers signed a nuclear deal, which addressed concerns over a potential nuclear breakout by Tehran. The S-300 system now being delivered by Russia is the result of a new deal signed with Iran in November, and is an upgraded version of the one that Tehran initially purchased. The delivery is expected to be complete by mid-2016.The deal was first signed in 2007, but was suspended by Russia under pressure from the US and Israel. Moscow said the delivery would destabilize regional security at a time when Tehran was accused of having a clandestine nuclear weapons program.