Russia will sign an agreement with India on October 15 on the delivery of S-400 Triumf antiaircraft missile systems, Russian presidential aide Yuri Ushakov said on Thursday.

"Following the results of the negotiations between our president and [Indian Prime Minister Narendra] Modi, an agreement will be signed on the delivery of S-400 Triumf antiaircraft missile systems to India, as well as some other documents," he said.

"Part of the documents will be signed behind closed doors," he said.

The Kremlin aide declined to comment on the details of the deal, suggesting that first the document should be signed.