"It's well known that the United States uses any possible ways of exerting pressure on its allies in all the issues… so, the US pressure on Turkey is by no means surprising", the diplomat said.
Grushko also noted that Russia was working on giving a prompt defence response to any threats related to US withdrawal from the Intermediate-Range Nuclear Forces Treaty.
The statement comes after US Vice President Mike Pence said on 3 April that Turkey had a choice either to remain a key NATO partner or undermine the alliance by the S-400 purchase.
In December 2017, Russia and Turkey signed a loan deal for the supply of S-400 air defence systems to Ankara. In early March, Turkish President Recep Tayyip Erdogan reaffirmed that the deal was completed and said a new deal on purchases of advanced Russian-made S-500 systems may be possibly concluded in the future.
The S-400 is Russia's next-generation mobile surface-to-air missile system and can carry three different types of missiles capable of destroying aerial targets at a short-to-extremely-long range. The weapon is created to track and destroy various types of aerial targets varying from reconnaissance aircraft to ballistic missiles.
