The Russian shipments of military aid to Syria have not materially changed in the last several years, but the shipments are expected to continue to rile Israel, with reports of more planned air defense systems to be delivered soon.
In 2013, Russia sent a Pantsir-S1 point air defense system to Syria, and plans to send a second set to Syria this year. These are the most advanced anti-aircraft missile systems in possession of the Syrian government, and since Israel is the only country really launching airstrikes against Syria’s government, it is seen as targeting them.
Though these shipments were planned for some time, Russia’s military aid to Syria has recently become a major issue, with the US in particular complaining about Russia’s support for the Syrian government. Russia has noted that the shipments are generally aimed at supporting Syria’s war against ISIS.
That’s the case with most of their shipments, indeed, but since ISIS doesn’t have an air force, the air defense systems clearly don’t have any real utility against them. Syria ordered the Pantsir-S1 systems in 2006, though most of the order has yet to be delivered.