Turkey has made progress in plans to procure an S-400 missile defense system from Russia and signatures have been signed, President Tayyip Erdogan.

“Steps have been taken and signatures signed with Russia concerning the S-400s. God willing we will see the S-400s in our country,” Erdogan told lawmakers from his ruling AK Party at a party meeting in parliament earlier this week.

NATO member Turkey said in April it had reached a “final stage” in talks to procure the air missile defense system.

Turkey will not be able to integrate the Russian S-400 into the NATO system, and its decision to purchase the Russian-made missile system has added to doubts about the health of Turkey's relationship with NATO and the European Union (EU).

The S-400 deal “is a clear sign that Turkey is disappointed in the US and Europe. But until the advance is paid and the assembly begins, we can’t be sure of anything,” Konstantin Makienko, an analyst at Moscow-based think tank the Center for Analysis of Strategies and Technologies, told Bloomberg earlier this month.

Western policymakers have also expressed consternation about the move.

“The problem is how do you interoperate in the NATO system with Russians? They’ll never interoperate,” US Defense Secretary James Mattis told reporters on July 14.

“We’ll have to see - does it go through? Do they actually employ it? Do they employ it only in one area? All that kind of stuff. But you know, we’ll have to take a look at it,” Mattis added.

The S-400 purchase includes an agreement allowing Ankara to produce some missiles domestically, which appears to further Turkey’s goal of developing the capacity of its own defense industry.

But Turkish President Recep Tayyip Erdogan has reportedly been frustrated with NATO over its response the July 2016 attempted coup against his government. Erdogan’s post-coup crackdown also led to the cancellation of foundering talks to join the EU, adding to the Turkish government's apparent resentment.

On July 16, Erdogan accused the EU of “messing us about,” citing the bloc’s broken promises over issues like visa deals and Syrian migrants. “We will sort things out for ourselves. There’s no other option,” he said.