Outgoing CIA director John Brennan has warned US President-elect Donald Trump to be more "disciplined" in his public pronouncements when he takes office on Friday 20 January, adding that "spontaneity is not something that protects national security interests".

"I think Mr. Trump has to be very disciplined in terms of what it is that he says publicly. He is going to be, in a few days' time, the most powerful person in the world," Brennan told Fox News Sunday. Trump has been known for his brash remarks, particularly on Twitter, where he can react to events in a way that seems off the cuff.

"I think he has to recognise that his words do have impact," Brennan said. "They can have very positive impact, or they can be undercutting of our national security." He added that Trump needs to understand the "implications and impact on the United States" that his remarks can have.

Brennan also took aim at the president-elect over remarks that seemed to equate the US intelligence community to Nazi Germany. In his press conference on Wednesday 11 January, Trump said it was "disgraceful" that the "false and fake" information of the unverified Trump dossier was allowed out by intelligence agencies: "That's something that Nazi Germany would have done, and did do."

Brennan said he took "umbrage" at the comment, which he called "outrageous".

When it comes to Russia, a country that has been dominating US headlines with the election hacking scandal and the recent allegations about Trump's links to the country, Brennan said that he doesn't think Trump "has a full appreciation of Russian capabilities, Russia's intentions, and actions that they are undertaking in many parts of the world".

Trump and the US intelligence community have had a rocky start to their relationship, beginning with the president-elect's wary and grudging acceptance of their conclusion that Russia attempted to influence the recent election and help him to defeat Democrat Hillary Clinton.