Russia has shipped a billion dollars’ worth of weapons to Syria since the civil war there began in 2011. Russia insists that this is not in violation of arms embargoes against Syria and are simply deliveries of weapons ordered before 2011. In the last year Syria has delivered over $200 million in cash to Russian banks to keep these weapons coming (mainly S-300 anti-aircraft systems and anti-ship missiles) and their warranties operational. These purchases are being paid for by Iran, which flies in the cash to a Syrian financial operation in Moscow. The cash is then delivered to Russian government accounts via a Moscow bank. The Syrian Moscow operation is run by an uncle of Syrian dictator Basher Assad.
These Russian shipments are not challenged by the international community because they are, technically, defensive weapons and cannot be used to attack the rebels. Another problem that is less clear is whether the weapons are being sent to Iran. That is illegal but without any clear evidence of such transfers there’s nothing anyone can do. The cash transfers are also illegal, since Iran is banned from the international banking system for anything involving weapons, oil sales, and military equipment in general. But no one is going to shut down air traffic between Iran and Russia.
Meanwhile, at least 14 Russian cargo ships arrived in Syria since 2011, plus numerous air freight flights. Recently Russia has quietly approved new shipments of small arms, which is forbidden but can be flown in and join similar weapons Syria had before 2011. Russia appears to believe that no one will challenge this either.