In addition, Turkey is in talks with Russia to purchase a second batch of the S-400 system, including coproduction and technology transfer options. If the S-400 system is operated in Turkey, Moscow could find a built-in cyber backdoor to spy on NATO assets.

The US president said a future US-UK trade agreement has “the potential to be far bigger and more lucrative” than any deal that could have been made with the EU.

The top U.S. military officer met in Switzerland with his Russian counterpart for talks aimed at increasing communication between their nations to reduce risks in conflict areas.