Israeli Prime Minister Benjamin Netanyahu traveled to Russia to discuss the situation in Syria with Russian President Vladimir Putin.

Netanyahu met Tuesday with Putin at his villa in the Black Sea resort of Sochi and was scheduled to return to Israel Tuesday evening before the start of the Shavuot holiday.

The meeting comes amid concerns by Israel that Russia is planning to sell the S-300 advanced air defense system to Syria.

Possession of S-300 missiles would significantly boost Syria’s ability to stave off intervention in its current civil war.

Russian Foreign Minister Sergei Lavrov said on May 10 that Russia would fulfill the contracts it has already concluded with Damascus, including air defense missiles and artillery systems; he did not specifically mention the S-300 advanced air defense system. However, Syria reportedly has already begun paying Russia for several S-300 systems under a current contract.

Israel also fears that the advanced air defense system could fall into the hands of the terrorist organization Hezbollah, based in southern Lebanon.