NATO chief Jens Stoltenberg said Thursday that relations between the military alliance and Russia had suffered a sharp deterioration and were now at their most difficult phase since the Cold War.

"I think (it) is correct to say that NATO's relationship with Russia is more difficult than it has been any time since the end of the Cold War," he said on CNN.

His comments come after US President Donald Trump said that ties between Washington and Russia had hit a "very dangerous" low.