Russia will reportedly hand over the first batch of the S - 300 surface - to - air defense missile system to Iran on Thursday. Iranian Defense Minister Brigadier General Hossein Dehqan, who is currently in Russia, will participate in a ceremony to deliver the first part of the defense system to Iran via the Caspian Sea on February 18, a source told Russia's Sputnik news agency. “Hossein Dehghan will participate in the ceremony of delivering the S-300 in Astrakhan on Thursday,” the source said. Dehqan’s trip to Moscow comes at the official invitation of his Russian counterpart Sergei Shoigu. The officials discussed the latest mutual, regional and international developments, as well as enhanced defense, military and technical cooperation between Tehran and Moscow on Tuesday. Russia committed to delivering the systems to Iran under a USD-800-million deal in 2007. Moscow, however, refused to deliver the systems to Tehran in 2010 under the pretext that the agreement was covered by the fourth round of the United Nations Security Council sanctions against Iran over its nuclear program. Following Moscow’s refusal to deliver the systems, Tehran filed a complaint against the relevant Russian arms firm with the International Court of Arbitration in Geneva. In April 2015, Russian President Vladimir Putin signed a presidential decree, paving the way for the long-overdue delivery of the missile defense system to Iran. The decision to deliver the system came after Iran and the P5+1 group of countries - the United States, France, Britain, China and Russia plus Germany - reached a mutual understanding on Tehran’s nuclear program in the Swiss city of Lausanne on April 2, 2015. Dehqan said earlier that “all changes” that have been made to the S-300 system by the Russians over the years will be implemented on the battalions that are going to be delivered to Iran.