US President Donald Trump has urged the justice department to investigate an anonymous New York Times article by an official in his administration.
He said Attorney General Jeff Sessions "should be investigating who the author of that piece was because I really believe it's national security".
Mr Trump also said he was considering taking action against the newspaper, causing its share price to dip.
But it is unclear what legal grounds any prosecutor could act on.
The Department of Justice said in response: "The department does not confirm, deny or otherwise acknowledge the existence or non-existence of investigations."
Meanwhile, the New York Times said in a statement: "We're confident that the Department of Justice understands that the First Amendment protects all American citizens and that it would not participate in such a blatant abuse of government power."
"The president's threats both underscore why we must safeguard the identity of the writer of this op-ed and serve as a reminder of the importance of a free and independent press."
Mr Trump was asked by reporters aboard Air Force One on Friday whether he was considering taking action over the New York Times op-ed.
"We're going to see," said Mr Trump, who was on his way to a rally in North Dakota. "I'm looking at that right now."
Members of his administration and inner circle from the vice-president downwards have been lining up to condemn the column and deny authorship.
Kentucky Senator Rand Paul has urged Mr Trump to conduct lie detector tests to find out who wrote the piece.
In Wednesday's column, the writer slammed Mr Trump's "amorality" and said a number of US officials were part of a "quiet resistance" inside the administration.
The author said they were "working diligently from within to frustrate parts of his agenda and his worst inclinations".
Mr Trump told Fox & Friends in an interview broadcast earlier on Friday that the op-ed was "unfair".
"What's unfair, I don't mind when they write a book and they make lies because it gets discredited," Mr Trump said.
He said it's more difficult "when somebody writes and you can't discredit because you have no idea who they are".