FBI Director James Comey looks on during the House Permanent Select Committee on Intelligence hearing on Russian actions during the 2016 election campaign on March 20, 2017 on Capitol Hill in Washington, DC.

Former FBI Director James Comey said he is not sure whether he believes President Donald Trump's denials about unsubstantiated dealings with prostitutes in Russia five years ago.

In an ABC News interview, Comey described briefing the then-president-elect on the salacious, unverified allegations that he watched prostitutes urinate on each other in Russia in 2013. The allegations came from what's known as the Steele dossier, which was funded in part by the Democratic National Committee.

"It was almost an out-of-body experience for me," Comey told ABC in an excerpt that aired Friday. "I was floating above myself, looking down, saying, 'You're sitting here briefing the incoming president about prostitutes in Moscow.'"

Trump, who fired the FBI director four months after that discussion, pushed back against the allegations, according to Comey. Trump said he was a "germaphobe" and suggested that someone like him wouldn't need to hire prostitutes, Comey said. The revelations come as the president is embroiled in multiple sex scandals.

When George Stephanopoulos, who interviewed the former FBI director for ABC News, asked Comey whether he believed Trump's denial of the allegations in the dossier, Comey said he couldn't be sure.

"Honestly never thought these words would come out of my mouth, but I don't know whether the current president of the United States was with prostitutes peeing on each other in Moscow in 2013," he said. "It's possible, but I don't know."

Comey said in his new book that Trump continually brought up the allegations about the prostitutes and suggested that the FBI investigate the claims. Comey said Trump told him that "it bothered him if there was 'even a 1 percent chance' his wife, Melania, thought it was true."

Comey's memoir, "A Higher Loyalty," is due out Tuesday. Excerpts of the book have already emerged, including details about how Comey and Trump discussed what's become known as the "pee tape."

Trump has also publicly denied the allegations in the dossier. On Friday, Trump took to Twitter to rip Comey, calling him an "untruthful slime ball" who "should be prosecuted."

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ABC News plans to air the full interview with Comey at 10 p.m. ET on Sunday night.