Russia's foreign minister has defended his country's sales of antiaircraft systems to Syria, insisting they are not banned by international law.

Speaking in Warsaw on Friday, Sergey Lavrov appeared to avoid saying clearly whether Moscow would sell Syria advanced S-300 batteries.

Israel has asked Russia to cancel what it says is an imminent sale of S-300 batteries to the Syrian government, arguing it would complicate the situation.

Asked by reporters whether Russia is planning to supply the S-300, Lavrov said: "Russia is not planning to sell. Russia has been selling for a long time, has signed contracts and is completing deliveries of technology that consists of anti-aircraft systems." Existing contracts are not believed to include the S-300.

Lavrov said the weapons are to help Syria defend itself against air attacks.