The FBI investigation into alleged links between Russia and the Donald Trump election team will carry on unimpeded by the sacking of its head, James Comey, his successor has said.
Acting Director Andrew McCabe told a Senate committee his boss's dismissal had not affected the work of the FBI.
He also said Mr Comey had "broad support" within the agency, which contradicted White House officials.
They contend Mr Comey was fired because the FBI had lost confidence in him.
And in his first sitdown interview since the firing, US President Donald Trump said Mr Comey was a "showboat" and a "grandstander" and the decision to let him go was his own.
The White House said Mr Comey's competence had come into question over the way he handled the case of Democratic Party election candidate Hillary Clinton's emails.
But critics accuse Mr Trump of sacking him for leading the Russia investigation.
"Director Comey enjoyed broad support within the FBI and still does to this day," Mr McCabe told the panel on Thursday.
"I can confidently tell you that the vast majority of employees enjoyed a deep and positive connection to Director Comey."
He also called the Russia inquiry a "highly significant investigation", countering the White House depiction of it as "probably one of the smallest things" that the FBI has "got going on their plate".
Mr McCabe also vowed not to update the White House on the status of the investigation and to notify the Senate panel of any attempt to interfere with the inquiry.
There were reports the ex-FBI boss had asked for more resources to conduct the probe and Democrats in the US Senate have formally requested details from the Justice Department on any additional funding he requested.
Some Democratic senators said they believed the reports to be true, although a Justice Department spokeswoman rejected them as "totally false".
Democrats have also called for a special prosecutor to take over the Russia investigation.
Trump on Comey: 'He's a showboat. He's a grandstander'
Mr Trump has insisted he is not under investigation, and he dismissed the FBI director he fired as a "showboat" and "grandstander".
Mr Trump also revealed to NBC News it was his decision to sack Mr Comey.
Mr Trump has dismissed the Russia probe as a "charade", a claim directly contradicted by Mr Comey's successor.
In his first interview since firing the FBI director, Mr Trump said he had asked Mr Comey whether he was under investigation.
"I said, if it's possible would you let me know, am I under investigation? He said, 'you are not under investigation'."
"I know I'm not under investigation," Mr Trump told the interviewer, repeating a claim he first made in a letter to Mr Comey, firing him.
The president also appeared to undercut the initial White House explanation that he fired Mr Comey on the recommendation of top justice officials.
"He's a showboat. He's a grandstander. The FBI has been in turmoil. I was going to fire Comey. My decision," Mr Trump said.
"I was going to fire regardless of recommendation."
Deputy Attorney threatened to resign - reports
Deputy Attorney General Rod Rosenstein was reportedly on the verge of resigning after the White House cast him as the prime catalyst for firing Mr Comey, US media reported.
He detailed Mr Comey's "serious mistakes" in a memo to President Trump, just prior to the firing.
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.
She maintained that Mr Trump "very much had been thinking about letting Mr Comey go since 9 November".
President Trump defended his actions on Wednesday, saying Mr Comey was fired "because he was not doing a good job".
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.