He also called Comey “a real nut job,” according to documents that summarized the meeting.
The document was read to the New York Times by U.S. officials.
Comey was fired on May 9. Trump met with Russian Foreign Minister Sergei Lavrov on May 10 in the Oval Office.
“I just fired the head of the F.B.I. He was crazy, a real nut job,” Trump said, according to the document.
“I faced great pressure because of Russia. That’s taken off.”
He also reportedly told them: “I’m not under investigation.”
A Democratic member of Congress, Ted Lieu, drew an instant conclusion about the implications, tweeting: “This. Is. Obstruction. Of. Justice.”
Spokesman Sean Spicer disputed not the facts of the report, but the interpretation, telling the Times that Trump was talking not about the criminal investigation, but about post-election scrutiny that was making it hard for him to work with Russia.
“By grandstanding and politicizing the investigation into Russia’s actions, James Comey created unnecessary pressure on our ability to engage and negotiate with Russia,” Spicer said in a statement to the Times.
Now Americans will hear from Comey.
In another news bomblet dropped on Friday afternoon, the turfed top-cop announced he will testify in an open hearing of the Senate intelligence committee at a date to be announced later this month.
Senior White House official under investigation
An official with close ties to Trump has been identified as a person of interest in the investigation into Trump’s campaign’s ties to Russia.
The Washington Post reported Friday that a White House advisor was under scrutiny by people familiar with the matter.
That means the probe has reached “into the highest levels of government,” the Post reports.
These latest accusations come as Trump has set out on his first international trip; he will be visiting Israel, Saudi Arabia and Italy (including the Vatican).
Trump has been facing criticism about reports that he leaked classified information to Russia as well as his handling of the announcement about the appointment of a special council to head the Russian probe.
The content of the leaked details in those reports, not to mention their simultaneous timing at a particularly vulnerable moment for the president, make it clear Trump has some enemies inside the U.S. government.
One hot topic of conversation in Washington these days is whether conservatives in town – weary of the Trump-related drama and longing for the comparative normalcy of a Mike Pence presidency – are preparing to abet his downfall.
Already, since the Comey firing, congressional committees controlled by the GOP have become more aggressive in seeking documents and witnesses, planting potential seeds for trouble to grow later.
“I think most of them are ready to flip,” one Democratic congressional staffer said of his Republican colleagues this week. A Republican staffer concurred: “The tide seems to be changing in town, right?”
WATCH: Foreign affairs experts call President Trump’s 1st trip abroad ‘ambitious’
Democrats, who have compared the widening scandal to the Watergate break-in and cover-up that in 1974 brought down Republican former President Richard Nixon, were quick to pounce on the latest reports.
Democratic Senator Edward Markey called them “seismic revelations,” and he questioned whether the United States might be heading into a constitutional crisis.
“This is an inflection point in the entire Russia collusion investigation,” he told MSNBC. “It makes it very clear that what Donald Trump was trying to do was to end the Russian investigation.”
“This is what OBSTRUCTION looks like: ‘I faced great pressure because of Russia. That’s taken off,'” Democratic Senator Patrick Leahy said on Twitter.
With files from Reuters and the Assocaited Press.