The inauguration of the US president-elect will take place on January 20.

"Spontaneity is not something that protects national security interests and so therefore when he speaks or when he reacts, just make sure he understands that the implications and impact on the United States could be profound," Brennan told the Fox News broadcaster.

The outgoing CIA Director also advised Trump to be careful when considering whether sanctions imposed on Russia should be lifted. On Friday, in an interview with The Wall Street Journal, Trump said that if Russia and Washington got along under his presidency, there would be no need for sanctions.

In November 2016, Trump won the US presidential election by gaining a major electoral lead over his rival, Democratic candidate Hillary Clinton.

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