"We took the decision to speed up the timetable for the delivery of these highly effective Russian systems," Putin told reporters after talks with Erdogan in the Turkish capital, referring to the S-400s but without giving a date.

He said that acceleration in production of the weapons was being done at the "request of our Turkish partners and friends".

The deal has been valued at about $2 billion according to reports.

Russian officials had said in December that the first deliveries of the S-400s were likely to begin at the end of 2019 or beginning of 2020

Such a major purchase of weaponry from Russia by a key NATO member had raised concerns both over Turkey's strategic orientation and the compatability of the systems within the alliance.

But Erdogan indicated that Turkey was in no mood to listen to criticism from the West over the purchase.

"This is a decision of Turkey. We made an agreement about the S-400s (with Russia) and this issue is now closed," he said.

According to Russian press reports, Turkey has also been hugely interested in a technology transfer and even joint production of the S-400s with Russia, a prospect that has been resisted by some in the Moscow security services.

But Putin refused to discuss the issue saying "these are exclusively commercial questions" rather than political ones.