the Russia-based international treaty organization that parallels NATO. The invitation came from the desk of then CSTO Secretary-General Nikolai Bordyuzha, who said that "the CSTO is an open organization. If Iran applies in accordance with our charter, we will consider the application." It was stated by a Western observer that the accession failed "basically due to the ayatollahs’ opposition to join a military bloc clearly dominated by a traditionally rival power of Iran such as Russia." Another Western observer points out that, like NATO, CSTO has a mutual defense treaty clause whereby attack against one is considered an attack against all and was concerned about the difficulty posed by a possible conflagration of the Iran-Israel variety. In November 2014 Sluzhba Vneshney Razvedki head Sergey Naryshkin floated the idea of admitting Iran as an observer to the CSTO Parliamentary Assembly. In 2010, Iran's refusal to halt uranium enrichment led the UN to pass a new resolution, number 1929 to vote for new sanctions against Iran which bans the sale of all types of heavy weaponry (including missiles) to Iran. This resulted in the cancellation of the delivery of the S-300 system to Iran: In September 2010 Russian President Dmitry Medvedev signed a decree banning the delivery of S-300 missile systems, armored vehicles, warplanes, helicopters and ships to Iran. Mahmoud Ahmadinejad criticised Russia for kowtowing to the United States. As a result of the cancellation, Iran brought suit against Russia in Swiss court and in response to the lawsuit Russia threatened to withdraw diplomatic support for Iran in the nuclear dispute. Since the outbreak of the Syrian civil war in 2011, Iran and Russia have become the Syrian government's principal allies in the conflict, openly providing armed support. Meanwhile, Russia's own relations with the West plummeted due to the Russo-Ukrainian War, the 2018 Skripal poisoning incident in Great Britain, and alleged Russian interference with Western politics, prompting the U.S. and Europe to retaliate with sanctions against Russia. As a result, Russia has shown a degree willingness to ally with Iran militarily. Following the JCPOA agreement, President Vladimir Putin lifted the S-300 ban in 2015 and the deal for the missile defense system to Iran was revived. The delivery was completed in November 2016 and was to be followed by a $10 billion deal that included helicopters, planes and artillery systems. In January 2021 Iran, China and Russia held their third joint naval