Concerned over President Donald Trump’s decision to fire FBI Director James Comey, the FBI reportedly opened an investigation into whether Trump was secretly working on behalf of Russia, according to a New York Times report published Friday night.

The bureau opened the counterintelligence inquiry days after Comey was ousted in May 2017, the Times reported, citing several people, including former law enforcement officials, familiar with the probe.

Investigators were specifically looking into whether Trump’s firing of Comey posed a national security threat as well as whether it was an obstruction of justice, considering the FBI’s broader investigation into Russia’s meddling in the 2016 presidential election.

Former law enforcement officials told the Times that the criminal aspect (whether Trump obstructed justice) and counterintelligence aspect (whether Trump was working covertly for Russia) of the investigation were combined into one inquiry because it would have been considered a national security threat if Trump had indeed ousted Comey to impede the Russia investigation.

According to the Times, Trump at least twice linked his decision to fire Comey with the Russia investigation, prompting counterintelligence officials to probe the president’s actions.

First, two days after Comey’s dismissal, Trump told NBC News’ Lester Holt that he had “this Russia thing” in mind when he decided to fire the FBI director.

“In fact, when I decided to just do it, I said to myself, I said: ’You know, this Russia thing with Trump and Russia is a made up story, it’s an excuse by the Democrats for having lost an election that they should’ve won,” the president told Holt at the time.

Second, Trump reportedly drafted a letter to Comey, slamming him for refusing to say that he wasn’t the focus of the Russia investigation.

Shortly after Comey was fired, special counsel Robert Mueller was appointed to oversee the broader investigation into Russia and the election. It’s unclear if Mueller is still investigating the counterintelligence inquiry into Trump.

Bloomberg via Getty Images The FBI opened an investigation into whether President Donald Trump’s firing of FBI Director James Comey posed a national security threat or amounted to an obstruction of justice, The New York Times reports.

Trump’s lawyer Rudy Giuliani told the Times he didn’t know of that probe while also downplaying it.

“The fact that it goes back a year and a half and nothing came of it that showed a breach of national security means they found nothing,” Giuliani said.

Trump continues to insist that there was “no collusion” between his campaign and Russia, while also dismissing the intelligence community’s assertion that Russia indeed interfered in the 2016 election.

Trump responded to the story in tweets early Saturday, saying that the FBI opened their probe “for no reason & with no proof” and slamming both Hillary Clinton and Comey. He did not deny the Times’ report.

I have been FAR tougher on Russia than Obama, Bush or Clinton. Maybe tougher than any other President. At the same time, & as I have often said, getting along with Russia is a good thing, not a bad thing. I fully expect that someday we will have good relations with Russia again! — Donald J. Trump (@realDonaldTrump) January 12, 2019

In another statement posted Friday night on Twitter by NBC News’ Geoff Bennett, White House press secretary Sarah Huckabee Sanders called the Times story “absurd,” arguing that Trump “has actually been tough on Russia.”

.@PressSec responds to @nytimes report that the FBI opened an inquiry into whether Trump was secretly working on behalf of Russia: pic.twitter.com/sAzRn7TIMJ — Geoff Bennett (@GeoffRBennett) January 12, 2019

Josh Campbell, former special assistant to Comey who resigned from the FBI in last year, told CNN on Friday that the Times’ report is alarming because of the level of approval the counterintelligence inquiry required.

“Those require the highest levels of approval from the Department of Justice,” Campbell told CNN. “This isn’t something that the FBI would open on its own. … This would require coordination with the Department of Justice.”

“This is a big deal when you think about the president of the United States being under FBI investigation,” Campbell added. “I don’t know if there’s any time in our lifetime or the history of the country where federal law enforcement looked down to the White House … and thought the actions of the president might threaten U.S. national security.”

Campbell left the FBI last February in response to the Trump administration’s attempts to discredit the bureau.

This article has been updated with a response on White House press secretary Sarah Huckabee Sanders’ comments.