"We are now discussing an additional delivery. We are in the advanced stage of talks and have settled almost all issues," Dmitry Shugaev, the director of Russia's Federal Service for Military-Technical Cooperation, told the Rossiya-24 television channel.
Turkey has acquired the weapons despite US and NATO warnings that they are incompatible with the alliance's defences. President Recep Tayyip Erdogan has said the surface-to-air systems will be put into service next month.
Shugaev also said that Russia planned to complete S-400 shipments to China by the end of this year. He said only one batch was left to be delivered under a 2014 contract, which is reported to cover six regimental sets worth over $3 billion.