 -- Explosive but unsubstantiated allegations suggesting Donald Trump was compromised by Russian agents and in league with Russian hackers appeared in a dossier given to the FBI in August by Democratic political operatives who later gave it to news organizations, including ABC News.

The document has circulated in the intelligence community and was reportedly raised last week during classified intelligence briefings to President Obama and President-elect Trump.

Trump and his aides expressed outrage yesterday that anyone would take the uncorroborated reports seriously.

“FAKE NEWS - A TOTAL POLITICAL WITCH HUNT!” Trump wrote on Twitter, in an apparent reference to the news reports.

On ABC News’ “Good Morning America,” Trump aide Kellyanne Conway slammed the allegations, saying, “Just to smear the president-elect of the United States, we now have intelligence officials divulging information that they are sworn not to divulge.”

“I don’t even think this is fake news, I think this is just fake. I would take the ‘news’ word right out of it,” she added.

Meanwhile, in Russia, Kremlin spokesman Dmitry Peskov has also been critical of the allegations, saying, “It’s an absolute spoof story. It’s absolute fabrication. It’s complete nonsense.”

Portions of the dossier outlining supposed ties between Trump’s team and Russian government agents started to surface over the summer based partly on information from a former British intelligence agent who was working for anti-Trump political operatives. The partisan operatives circulated portions of the documents to federal officials and reporters, including to ABC News, both before and after the 2016 election.

Eventually, Republican Sen. John McCain received a copy and forwarded it directly to FBI Director James Comey.

Comey was pressed during hearings on Capitol Hill on Tuesday as to whether the FBI is investigating the allegations. He declined to answer, citing agency policy. But a senior official briefed on the case said the allegations were too serious to ignore.

Among the claims are allegations that Trump was personally compromised by the Russians during a 2013 trip to Moscow and that Trump aides were later involved with the Russians’ hack of the Democratic Party. Some specific allegations have brought sharp denials.

A Trump lawyer named in the report, Michael Cohen, called “laughably false” the assertion that his Ukrainian-born father-in-law had a dacha near Russian President Vladimir Putin’s. “I don’t even think my father-in-law has ever been to Moscow,” Cohen told ABC News. “I wonder who’s living in the dacha.”

Another suggestion in the documents given to the FBI — that Cohen supposedly met with the Russians in Prague, Czech Republic, last August — is also false, he said.

“I’ve never actually walked the land in Prague, and last August I was not in Prague,” he said.

The dossier provides no back-up evidence, but the claims were hard to ignore, officials told ABC News. And the allegations gained currency in intelligence and law enforcement circles as Trump continued his unorthodox defense of Russian hacking and unrestrained praise of Putin.

In May, Trump said he “respects Putin,” calling him “a strong leader.”

And, despite the consensus of the nation’s top intelligence agencies, Trump has continued to question whether Russia had a hand in the hacking of Democratic National Committee computers.

“I don’t think anybody knows it was Russia that broke into the DNC,” he said at one point.

David Kramer, a Russia expert who served as an assistant secretary of state under George W. Bush, said he was “surprised by Mr. Trump’s public admiration for Mr. Putin.”

“Generally Republicans have taken a harder line toward Russian aggression, toward Russian human rights abuses, toward any Russian efforts in interfering in other countries’ internal affairs,” Kramer said. “It is not generally consistent with what I myself have experienced and what I have seen from others, so it raises some questions in my mind about what’s driving it.”