US lawmakers have called on President Donald Trump to turn over any tapes of conversations with fired FBI chief James Comey.
This could potentially trigger a showdown with the White House as Democrats consider a boycott of the vote on Comey's replacement.
In a highly unusual move, Mr Trump last week appeared to suggest he might have tapes of conversations with Mr Comey and warned the former FBI director against talking to the media.
Mr Trump and a White House spokesman declined to confirm or deny whether such tapes exist.
Republican Senator Lindsey Graham of South Carolina said the White House must "clear the air" about whether there were any taped conversations.
"You can't be cute about tapes. If there are any tapes of this conversation, they need to be turned over," he said.
Mr Trump sparked a political firestorm when he abruptly fired Mr Comey last week. The FBI has been investigating alleged Russian meddling in the US election and possible ties between Moscow and the Trump campaign.
Democrats have accused Mr Trump of attempting to thwart the FBI's probe and have called for some type of independent inquiry into the matter.
Mr Trump has said he removed Mr Comey because he was not doing a good job and that Mr Comey had lost the support of FBI employees - something rejected by the acting head of the agency.
Mr Trump tweeted on Friday that "James Comey better hope that there are no 'tapes' of our conversations before he starts leaking to the press!"
If there were recordings, Republican Senator Mike Lee said it was "inevitable" that they would be subpoenaed and the White House would have to release them.
Mr Lee said recording conversations in the White House was "not necessarily the best idea."
Special prosecutor would bring 'sigh of relief'
Mr Trump's threat about tapes has intensified calls from Democrats for an independent probe of alleged Russian meddling in the US election.
Senate Democratic Leader Chuck Schumer said Mr Trump must immediately provide Congress with any tapes and warned that destroying existing tapes would violate the law.
Mr Schumer also said Senate Democrats are weighing whether to refuse to vote on a new FBI director until a special prosecutor was named to investigate Mr Trump's potential ties to Russia.
Russia has denied the claims and the White House said there was no collusion.
"To have that special prosecutor, people would breathe a sigh of relief because then there would be a real independent person overlooking the FBI director," Mr Schumer said.
Mr Trump, who has sought better relations with Russia, has continued to question whether it was behind the hacking of email accounts belonging to Democrats involved in Hillary Clinton's 2016 presidential campaign.
However, Secretary of State Rex Tillerson said there was no question that "the Russians were playing around in our electoral processes".
Justice Department interviewing candidates
The Justice Department began interviewing candidates for the FBI director job on Saturday.
Some people under consideration include acting FBI Director Andrew McCabe, Republican Senator John Cornyn of Texas, New York Appeals Court Judge Michael Garcia and former Assistant Attorney General Alice Fisher, according to a White House official.
If a Senate vote on a new FBI director breaks down along party lines, Democrats would not have the votes to block a nominee because Republicans hold a majority in the chamber.
"The key is getting some of our Republican colleagues to join us," Mr Schumer said.
Republican leaders in the Senate have rebuffed calls for a special prosecutor, saying it would interfere with ongoing congressional probes.
Mr Graham said there may come a time when a special prosecutor was needed, but not now.
"Right now, it is a counterintelligence investigation, not a criminal investigation. So you don't need a special prosecutor," he said.