The US envoy to NATO has warned Turkey not to purchase a new arms system from Moscow, Bloomberg reported.

“We are very concerned about any kind of Russian missile defense in one of our alliance countries,” US Ambassador to NATO Kay Bailey Hutchison said during a Tuesday call with reporters, a day before the alliance’s defense ministers meet in Brussels. “The whole alliance is concerned about this, and we hope that Turkey will make the right decision and look for another system.”

Turkey finalized plans to buy the Russian system, called the S-400, last year, with the first delivery scheduled for October 2019.

If Turkey does purchase Russian arms, it could put at risk the types of defenses other NATO allies could have in the country, affect the inter-operability of defense systems and violate security and intelligence among alliance members, Hutchison said.

President Recep Tayyip Erdoğan has been adamant that Turkey would buy the Russian missile system, saying its traditional allies in the West had failed to meet his country’s defense needs.