Turkey has signed a deal with Russia to buy S-400 antiaircraft missile systems in its first major weapons purchase from Moscow.
Turkish newspapers on September 12 quoted Turkish President Recep Tayyip Erdogan as saying the deal was signed a deposit payment has been made.
Vladimir Kozhin, an aide to Russian President Vladimir Putin, confirmed that the contract was signed, saying it "is being prepared to be fulfilled."
Kozhin said "all the decisions made for the contract strictly comply" with Russia's strategic interests.
Erdogan said he and Putin were "determined on this issue."
The accord, Ankara's most significant weapons purchase from a non-NATO supplier, has raised concerns in the West over technical compatibility with NATO equipment.
The Pentagon has said it is "generally a good idea" for NATO allies to buy inter-operable equipment.
But Erdogan insists that Turkey is free to make military acquisitions based on its defense needs.
"We make the decisions about our own independence ourselves," Erdogan said on September 12. "We are obliged to take safety and security measures in order to defend our country."