President Donald Trump has condemned his former lawyer Michael Cohen amid US media reports that he secretly recorded Mr Trump discussing payments to former Playboy model Karen McDougal.
The tapes were reportedly discovered during an FBI raid on Mr Cohen's property earlier this year in New York.
Mr Trump tweeted that such a raid was "almost unheard of".
He added that a lawyer secretly recording a client was "totally unheard of and perhaps illegal".
The president also insisted he had done nothing wrong.
Mr Cohen's lawyer responded by saying that Mr Trump's statement was "false".
What is the tape said to reveal?
The New York Times reports that in the recording, Mr Trump and Mr Cohen discuss paying Ms McDougal, who says she had a 10-month affair with Mr Trump in 2006, a year after he married his current wife Melania.
The tape was reportedly made two months before the November 2016 election that saw Mr Trump become president.
In the lead-up to the vote, Ms McDougal sold her story to the National Enquirer magazine, which is owned by a personal friend of Mr Trump.
She says a $150,000 (£115,000) agreement gave the tabloid exclusive story rights and banned her from talking publicly about the alleged affair. But the Enquirer did not publish her story after paying for the rights.
Why is this an issue?
The Department of Justice is looking into alleged hush money paid to women who claim they had a relationship with Mr Trump.
It is suggested that such payments, if proved, would amount to an election expense.
Failing to declare election expenses is a crime.
Federal investigators have reportedly demanded the tabloid's records on the McDougal payment.
In May, President Trump admitted that he had reimbursed Mr Cohen for a payment he made to another woman to hush up her claims of an affair.
Mr Trump had previously denied all knowledge of the $130,000 payment to porn actress Stormy Daniels as part of a non-disclosure agreement.
Mr Cohen, who has not been charged with any crime, is reportedly under investigation for possible bank and tax fraud, as well as potential violation of election law.
He has declined to comment publicly on the tape story.
But his lawyer, Lanny Davis, said in a brief statement on Friday that he was "sensitive" to the ongoing investigation before adding: "Suffice it to say that when the recording is heard, it will not hurt Mr Cohen.
"Any attempt at spin cannot change what is on the tape."
Mr Trump and his aides have consistently denied he had an affair with Ms McDougal, or had any knowledge of any payment to her.