New Acting FBI Director Andrew McCabe acknowledged for the first time in public testimony Thursday that some agents were angry with the 2016 decision not to prosecute Hillary Clinton – while also defending ousted Director James Comey’s overall standing at the bureau.

“I think morale's always been good, but there were folks within our agency that were frustrated with the outcome of the Hillary Clinton case and some of those folks were very vocal about those concerns,” McCabe testified.

McCabe stepped into the role of acting director Wednesday after Trump dismissed Comey, purportedly over his conduct during the 2016 probe into Clinton's use of a private email server as secretary of state. Comey announced at a press conference last July that, despite concluding Clinton had been “extremely careless” in the handling of classified material, he would not recommend prosecution.

McCabe’s comments at the Senate Intelligence Committee hearing mark the first public recognition from the FBI that some agents were angry at the decision not to prosecute.

While he noted the anger over that decision, he also pushed back on White House claims that Comey had lost confidence from rank-and-file staff in the agency.

"I can tell you also that Director Comey enjoyed broad support within the FBI and still does to this day," he testified, adding that many staff held a "deep, positive connection" with him.

Democrats and some Republicans have expressed concern at the timing of Comey’s firing, with some questioning whether it was related to the FBI probe into alleged ties between Russian officials and Trump associates during the presidential campaign.

But McCabe told senators that the investigation – which he called “highly significant” -- is continuing unimpeded.

"The work continues despite any changes in circumstances," McCabe said. "There has been no effort to impede our investigation to date. You cannot stop the men and women of the FBI from doing the right thing, protecting the American people and upholding the Constitution."

Comey originally had been set to testify Thursday about worldwide threats, but McCabe appeared in his place, offering assurances to lawmakers that if there was any interference he would inform them. When asked by Sen. Mark Warner, D-Va., if he would promise to tell them of any moves to interfere in the probe, McCabe said: “I absolutely do.”

McCabe also denied reports that Comey had requested more resources for the Russia probe in the days leading up to his termination, with McCabe saying he believes the probe to be “adequately resourced” and adding that normally the FBI will not request resources for a single investigation.

Earlier in the hearing, McCabe declined to confirm if Comey had told Trump that he was not the subject of an investigation by the FBI. McCabe told Chairman Sen. Richard Burr, R-N.C. he couldn’t comment on conversations between the two.

In his letter to Comey informing him of his dismissal, Trump said that Comey had told him on three occasions that he was not the subject of any probe. At the hearing, McCabe later said he would not give such updates to Trump.

Fox News' Wes Barrett and Catherine Herridge contributed to this report.