Ousted FBI Director James Comey is willing to speak with Congress but only if the testimony is not behind closed doors, according to a source close to him.

Comey had been invited to speak to the Senate Intelligence Committee next week but turned down the invitation hours after President Donald Trump tweeted a warning to him that he "better hope that there are no 'tapes'" before he started "leaking to the press."

But, The New York Times reports, Comey is willing to speak if his testimony is made public.

So far, Comey has only responded to his sudden dismissal through a short letter to his former colleagues, in which he wrote that he has "long believed that a President can fire an FBI Director for any reason, or for no reason at all. I'm not going to spend time on the decision or the way it was executed. I hope you won't either."

Former FBI agent Clint Watts, who testified before the Senate Intelligence Committee in March concerning Russian interference into the election, said Saturday he would like to see Comey testify, but agreed that it should not happen behind closed doors.

"I would be thrilled for him to have a public hearing," Watts told MSNBC. "I would like to hear his version of it. I think the smartest thing I've heard all week is him saying I'll show up but only do it in public. He's smart not to be in a closed hearing on the matter."

Trump fired Comey, who was appointed by President Barack Obama to a 10-year-term in 2013, on Tuesday, about a week after the former FBI director told a Senate hearing that he felt "mildly nauseous" that his actions in the Hillary Clinton email case may have affected the 2016 presidential election.

Initially, Trump's representatives said the firing was spurred by a report from Deputy Attorney General Rod Rosenstein but on Thursday the president said he'd already decided to let Comey go.

Comey will most likely face questions from the Senate committee about both the probe into alleged Russian collusion with Trump's presidential campaign and about the timing behind his surprise firing.