The director of the CIA has warned Donald Trump it would be “disastrous” to tear up the US’s nuclear deal with Iran, after the President-elect pledged to do so during his successful election campaign.

John Brennan said abandoning the deal, which was signed by President Barack Obama in 2015 after years of negotiations, would make nuclear proliferation in the Middle East more likely.

Speaking to the BBC in the first foreign media interview by a CIA director, Mr Brennan said: “It would be the height of folly if the next administration were to tear up that agreement.

“It could lead to a weapons programme inside of Iran that could lead other states in the region to embark on their own programmes.”

Mr Brennan will step down after four years as CIA director in January, just as Mr Trump is inaugurated as the 45th President.

And after repeated accusations that Russia was involved in influencing the course of the election, Mr Brennan warned Mr Trump to be wary of “promises” coming from Moscow.

He said he could not comment on the impact of Russian state-sponsored hacking and releasing of information during the race for the White House, when Hillary Clinton and the Democratic party were repeatedly targeted by cyberattacks.

But he did confirm that Russia tried to carry out such activity, and that he had spoken with his Russian counterparts to challenge them over the matter, warning them such attacks would backfire.

Mr Trump has repeatedly said he will seek a better working relationship with Russian President Vladimir Putin, describing greater ties between the two superpowers as being only a good thing.

"I hope there is going to be an improvement in relations between Washington and Moscow," Mr Brennan said.

But he warned: "President-elect Trump and the new administration need to be wary of Russian promises. Russian promises in my mind have not given us what it is that they have pledged.”

Russia, the CIA chief said, was responsible alongside the Syrian government for the “outrageous” slaughter of civilians in Aleppo. He accused Moscow of being “disingenuous” in its efforts to drag out Syria peace talks in an effort to “choke” the besieged city.

“Russia is a country that will pursue its national interests, frequently to the detriment of the interests of the people in the countries wherein it operates,” he said.

And Mr Brennan cautioned the Trump transition team on the need to be more “disciplined” in their public statements about the US’s role in the world.

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It comes after Mr Trump’s new national security adviser, General Michael Flynn, said the US needed to recognise it was in a “world war” with Islamist militants.

Asked if such language was helpful, Mr Brennan said the President-elect and his team needed to be "disciplined in the language that they use (and) the messages that they send”.