US President-elect Donald Trump has been warned against scrapping a historic deal with Iran aimed at preventing the country from developing nuclear weapons.
Under a deal with the US and five other world powers in 2015, Iran agreed to scale back its nuclear programme in exchange for easing of sanctions on its finances and oil industry.
During the presidential campaign, Trump promised to dismantle or revise US position on the deal.
But in an unusual public warning, the country's intelligence chief said that the potential move would be "disastrous".
"I think it would be the height of folly if the next administration were to tear up that agreement," CIA director John Brennan told the BBC in an interview aired on Wednesday.
"It would be disastrous, it really would," he added.
He said it would be "almost unprecedented" for one administration to tear up an agreement made by a previous one.
Brennan warned "it could lead to a weapons programme inside of Iran that could lead other states in the region to embark on their own programmes".
Since his election, Trump has been more circumspect, not publicly discussing the international deal with Tehran.
But his pick to succeed Brennan as head of the CIA, Mike Pompeo, is a vocal critic of the agreement.
Brennan also expressed hope there would be an improvement in relations between Washington and Moscow.
But he warned: "I think 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 they had pledged."
During the presidential campaign, Trump had also said he might authorise the torture of detainees, including waterboarding, to gain information, but has since said he had received advice that made him rethink his approach.
"I would counsel my successor not to go down that road any more," Brennan said.
"Without a doubt the CIA really took some body blows as a result of its experiences in the detention interrogation programme.... I think the overwhelming majority of CIA officers would not want to get back into that business."