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

Mr. Brennan told the BBC that the United States should continue to support moderate rebels fighting Mr. Assad’s forces in Syria as a bulwark against the “onslaught” meted out by the Syrian government and its allies, Russia, Iran and Hezbollah.

Alluding to the ferocious fighting in recent days in the Syrian city of Aleppo, which has seen thousands of civilians flee for their lives, he said Russia had failed to show that it was a dependable negotiating partner and had prolonged the discussion process with the aim of choking the city.

“I do not have confidence that the Russians are going to relent until they are able to achieve as much tactical battlefield successes as possible,” he said.

Mr. Brennan also took a strong stand against waterboarding, which he said had undermined the C.I.A. The agency came under fierce international criticism after using interrogation methods like waterboarding in the aftermath of the Sept. 11, 2001, attacks in the United States, and Mr. Obama has since banned the practice.

During the campaign, Mr. Trump pledged to bring back waterboarding and said he was open to unspecified methods he characterized as “a hell of a lot worse.” And even as he indicated in an interview last week with the The New York Times that he had heard persuasive arguments that torture was not effective, he has left the option open.

Mr. Brennan warned that the use of waterboarding would be rejected by most officers at the C.I.A. “Without a doubt, the C.I.A. really took some body blows as a result of its experiences,” he told the BBC. “I think the overwhelming majority of C.I.A. officers would not want to get back into that business.”