US President Donald Trump has called on the US Justice Department to investigate the New York Times after it published a column this week by an anonymous administration official questioning his fitness for office.
Mr Trump also said he was considering taking action against the newspaper, whose shares moved briefly lower after his comments were made public.
Mr Trump told reporters aboard Air Force One "Were going to see. I'm looking at that right now."
He said that Attorney General Jeff Sessions "should be investigating who the author of that piece was because I really believe it's national security".
Mr Trump did not indicate what sort of action he was considering against the newspaper and it was unclear what legal grounds he could act on.
A Justice Department spokeswoman said the department does not confirm or deny investigations.
The New York Times could not be immediately reached for comment.
A number of top Trump advisers have disavowed the piece, which was published on Wednesday without a name in what the newspsper said was a rare but necessary move to protect the writer.
In the column, the writer criticised Trump's "amorality" and leadership style.
The official said there were a number of US officials who were part of an "quiet resistance" inside the administration who were "working diligently from within to frustrate parts of his agenda and his worst inclinations".
Mr Trump described the anonymous New York Times article as "horrible".
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Speaking at a rally in Montana last night, Mr Trump questioned if it was subversion or treason and claimed that even liberals who hate him thought it was terrible.
Mr Trump said the anonymous writer of The New York Times article was a gutless coward as he addressed crowds.
He said that the newspaper should publish the person's name for the sake of national security and that unelected, deep state operatives were a threat to democracy.
The New York Times said the article was written by a senior official in the Trump administration.
The writer claims staff are alarmed at the president's erratic behaviour and that there was a resistance within the administration.
The Times acknowledged the "rare step" of publishing an anonymous editorial but said the official's job would be jeopardised if they were identified.
The piece described a "two-track" presidency in which Mr Trump says one thing and his staff consciously does another, citing the president's alleged preference "for autocrats and dictators".
Are the investigative "journalists" of the New York Times going to investigate themselves - who is the anonymous letter writer?
— Donald J. Trump (@realDonaldTrump) September 6, 2018
The basis of the anonymous op-ed piece in Wednesday's New York Times is also supported by a new book by veteran journalist Bob Woodward.
Drawing on hundreds of hours of interviews, the respected White House chronicler describes a coalition of like-minded aides plotting to prevent the US President from destroying the world trade system, undermining national security and sparking wars.
The US President has described the book as a "scam," alleging that it includes made-up quotes.
"The Woodward book is a scam. I don't talk the way I am quoted. If I did I would not have been elected President. These quotes were made up. The author uses every trick in the book to demean and belittle," Mr Trump tweeted.
Elsewhere, former US president Barack Obama launched a blistering critique of Mr Trump and Republicans and urging Democrats to vote in November's elections to restore "honesty and decency and lawfulness" to government.
Additional reporting: Brian O'Donovan
