Trump said Turkey was forced to buy the S-400 system by his predecessor Barack Obama, leading the Pentagon to halt plans to sell F-35 fighter jets to the country.

"I've had a good relationship with President (Recep Tayyip) Erdogan," Trump told journalists.

"It's a very tough situation that they're in and it's a very tough situation that we've been placed in.... With all of that being said, we're working through it -- we'll see what happens."