Former FBI Director James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE said late Thursday that claims by President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE and his allies that the FBI improperly spied on his presidential campaign were made up.

"As best I can tell, it's made up. I don't know where he's getting that from, honestly," Comey told late-night host Conan O'Brien during an interview on Thursday night.

Asked if it was possible that there was a "spy" inserted into Trump's campaign by an intelligence agency, Comey said, "I don’t find it possible and I know it not to be true."

Clapper has now admitted that there was Spying in my campaign. Large dollars were paid to the Spy, far beyond normal. Starting to look like one of the biggest political scandals in U.S. history. SPYGATE - a terrible thing! — Donald J. Trump (@realDonaldTrump) May 24, 2018

The president and his allies have said in recent days that the FBI used a top-secret informant to spy on the Trump campaign for political purposes.

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The informant, who has been identified in media reports as Stefan Halper, an American professor, reportedly met with at least three Trump campaign advisers in 2016: George PapadopoulosGeorge Demetrios PapadopoulosTale of two FBI cases: Clinton got warned, Trump got investigated Trump says he would consider pardons for those implicated in Mueller investigation New FBI document confirms the Trump campaign was investigated without justification MORE, Sam Clovis and Carter Page.

Trump has asserted that if the FBI did spy on his campaign it would be "bigger than Watergate," the scandal that prompted the resignation of former President Nixon.

Comey remarked Thursday that Trump has repeatedly declared something to be "the biggest scandal since Watergate."

"My guess is two weeks from now it'll be something different than this," Comey said.

No evidence has surfaced that suggests the Obama administration spied on Trump's campaign.

Select lawmakers met with top Justice Department officials in two separate meetings on Thursday to discuss highly classified information about the FBI's use of the informant in 2016.

Trump abruptly fired Comey in May 2017, ostensibly for his handling of the FBI investigation into Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE's use of a private email server during her tenure as secretary of State. Since then, the president has repeatedly accused the former top cop of corruption.

In a tweet Thursday morning, Trump accused Comey of dealing significant damage to the FBI, calling him a "terrible and corrupt leader."

Comey has pushed back against Trump's broadsides during a series of public appearances and media interviews to promote his book, "A Higher Loyalty: Truth, Lies, and Leadership." In that title, Comey calls Trump an unethical and self-interested leader, who is "untethered to truth."