The White House says it is unaware whether the deputy attorney general threatened to quit after he was blamed for the FBI chief’s sacking.
Rod Rosenstein reportedly was on the verge of resigning after the White House cast him as the prime catalyst to fire James Comey, US media reported.
He detailed Mr Comey’s “serious mistakes” in a memo to President Donald Trump, just prior to the firing.
The sacking of Mr Comey has ignited a firestorm of criticism.
Democrats have called for a special prosecutor to take over the probe of alleged links between the Trump election team and Moscow, which Mr Comey was heading.
Mr Rosenstein reportedly made his threat unless the White House conveyed that the decision began with the president, according to US media.
“I’m not aware of his threatening to resign,” White House Deputy Press Secretary Sarah Huckabee Sanders said on ABC’s programme Good Morning America on Thursday.
Lawmakers in Washington are reeling after the White House abruptly removed Mr Comey on Tuesday for his handling of the inquiry over Hillary Clinton’s emails.
Critics accuse the Republican president of firing the nation’s top law enforcement official because he was leading the Russia inquiry.
She maintained that Mr Trump “very much had been thinking about letting Mr Comey go since 9 November”.
Senior Democrats have also said they believed Mr Comey had recently asked the justice department for more resources for the FBI Trump-Russia investigation, which they say could have prompted his dismissal.
The White House has rejected the calls to appoint a special prosecutor to investigate allegations the Trump campaign colluded with the Kremlin over last year’s election.
The Senate Intelligence Committee has also invited Mr Comey to testify next week.
In a farewell letter to staff, Mr Comey said he would not “spend time on the decision or the way it was executed”.
“I have long believed that a president can fire an FBI Director for any reason, or for no reason at all,” he wrote.
President Trump defended his actions on Wednesday, saying Mr Comey was fired “because he was not doing a good job”.
But Democratic senator Dianne Feinstein said she “understood” that Mr Comey had asked Mr Rosenstein for more resources for the FBI investigation.
Another Democratic Senator, Richard Durbin, told US media be believed the reports to be true, although Justice department spokeswoman Sarah Isgur Flores rejected them as “totally false”.
Republicans and Democrats vowed the House and Senate Intelligence Committees’ investigations into the Russia claims would continue.
The Senate Intelligence Committee moved forward by issuing a rare subpoena for documents from Michael Flynn, Mr Trump’s former national security adviser, after he rejected its request to do so in April.
Mr Flynn, a retired army lieutenant-general, misled the White House about discussing US sanctions against Russia with the country’s envoy, Sergei Kislyak, before Donald Trump’s inauguration in January.
His links to Russia are being scrutinised by the FBI and the House and Senate Intelligence Committees, as part of wider investigations into claims Moscow sought to tip the election in favour of Mr Trump, and into contacts between Russia and members of the president’s campaign team.
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