(Bloomberg) -- Turkey and Russia discussed expanding defense cooperation from missiles to ships, warplanes and submarines, Turkish President Recep Tayyip Erdogan said, defying threatened U.S. sanctions. 

Erdogan’s comments on potentially tighter defense ties with Russia could alarm Turkey’s NATO allies, already anxious over Ankara’s purchase of Russia’s S-400 missile defense system, and follows Erdogan’s complaint last week that relations with the U.S. remain strained. 

The Turkish leader, who met with Russian President Vladimir Putin in Sochi on Wednesday, said they discussed in detail how to move ahead on S-400 cooperation. Turkey and Russia have been discussing technology transfers and local production ahead of a potential Turkish acquisition of a second S-400 system. 

Russia, which built Turkey’s first nuclear plant on the Mediterranean coast, will also evaluate Ankara’s offer to jointly construct two more, Erdogan said. 

Erdogan Says Ties With U.S. Strained, Talks Up Russia Links

“Our agenda mainly focused on how we can further develop Turkey-Russia relations, the joint steps we can take from the defense industry to political and military issues, and the investments we can make together,” the Turkish leader said, according to Turkish media reports. “We also had the opportunity to discuss what kind of steps we will take on jet engines, warplanes,” ships and submarines, he added, expressing dissatisfaction with a joint submarine construction project with Germany. 

While in New York last week, Erdogan told CBS TV that he intends to press ahead with the S-400 program. On the eve of Erdogan’s meeting with Putin, U.S. senators warned Turkey that additional Russian missile purchases would trigger new sanctions. 

U.S. Senators Vow Sanctions If Turkey Buys New Russian Missiles

The U.S. has already imposed penalties on Turkey’s defense industry over the initial missile purchase, saying the Russian system could be used to gather intelligence on Lockheed Martin Corp.’s F-35 stealth jet. It previously suspended Turkish defense contractors from the international program to help build the F-35.

Turkey has so far refused to jettison the first S-400 battery it acquired in 2019.

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