The acknowledgement came as MSNBC host Rachel Maddow said she has obtained part of Mr Trump's 2005 tax forms, and prepared to discuss the document on her Tuesday night show.

The records have become highly sought-after because Mr Trump refused to release his returns during the campaign, breaking a decades-long tradition.

He claimed he was under audit by the Internal Revenue Service and said his lawyers had advised against it - though experts and IRS officials said such audits do not bar taxpayers from releasing their returns.

The White House hit back pre-emptively on Tuesday night, saying that publishing those returns would be illegal.

"You know you are desperate for ratings when you are willing to violate the law to push a story about two pages of tax returns from over a decade ago," the White House said.

The unauthorised release of federal tax returns is a criminal offence. But Ms Maddow argued that MSNBC was exercising its First Amendment right to publish information in the public interest.

Mr Trump has long insisted the American public was not interested in his returns and said little could be learned from them.

But his full returns would contain key details about things like his charitable giving and how much he made each year.

The issue was a major campaign point of attack from his rival Hillary Clinton, who suggested Mr Trump had something to hide.

The White House has not said whether or not the president plans to release his returns while he is in office.

More than a million people have signed a White House petition urging Mr Trump to release them.