Collins is referring to Trump's joint press conference with the President of Romania from Friday, during which Trump was asked if the tapes exist, only to respond, "I'll tell you about that maybe sometime in the very near future".
Detailing one-on-one talks with a sitting president - which under normal circumstances are private - Comey said he took painstaking notes for fear Trump might "lie" about the unusual encounters.
The White House has repeatedly tried to shift the focus away from the content of Comey's allegations and onto the manner of their release.
Comey had been leading an FBI investigation into several Trump aides and their contacts with the Russian government - which United States intelligence agencies say tried to tilt the 2016 election in Trump's favor - before being fired.
Republican Senator Susan Collins called on Sunday for Trump to "voluntarily turn them over" to the Senate Intelligence Committee and to the special counsel, Robert Mueller, investigating possible collusion between Trump aides and Russian Federation.
Comey refused to comment on whether he thought Trump was trying to block justice.
Trump fired Comey in May, setting off a series of events that eventually led the career law enforcement official to sit before senators on Thursday. He said the recently appointed special counsel would examine the matter.
"This is an issue that the president should have cleared up in his press conference", Collins said on CNN. That, Comey said, anxious him.
It is likely that he will answer questions about the committee's investigation of Russia's alleged interference in the 2016 presidential election.
"Although the law requires no reason at all to fire an Federal Bureau of Investigation director, the administration then chose to defame me and more importantly the Federal Bureau of Investigation by saying that the organization was in disarray, that it was poorly led, that the work force had lost confidence in its leader", he charged.
Australia Reaches $53 Million Settlement With Refugee Detainees
The lead plaintiff, Majid Karami Kamasaee, was detained on Manus Island for 11 months from September 2013. All migrants arriving to Australia without a visa are subject to mandatory detention.
Trump, who said he was willing to testify under oath about the claims made Thursday, also refuted Comey's statement that he asked the former FBI director to end the investigation into former national security adviser Michael Flynn.
"This is not privileged information", Dean said bluntly.
"Those were lies, plain and simple", Comey said, firing a shot of tension through the hearing room, which stood silent except for the shutter clicks of photographers capturing the political theater.
Ahead of the hearing, Comey described his mounting discomfort in the weeks leading up to his dismissal as Trump pulled him aside in person and phoned to press him on the investigation.
But Trump's denunciations of Comey have only fueled demands that the president - who has denied asking for loyalty or urging that the investigation be shelved - give his account under oath. "But we were very, very happy and, frankly, James Comey confirmed a lot of what I said, and some of the things that he said just weren't true", Trump said.
"The president said, 'I need loyalty, I expect loyalty.' I didn't move, speak, or change my facial expression in any way during the awkward silence that followed", Comey said.
In an angry early-morning tweet from his New Jersey golf club, the embattled president questioned Comey's character and whether he had broken the law in revealing their conversations.
But Republican House Speaker Paul Ryan appeared to sympathize with Trump.
"And my bigger concern is we look and say we hold our leaders accountable and we need all the information to hold them accountable".