US President Donald Trump yesterday questioned the release of his 2005 tax documents, blasting the reporter who acquired the returns after months of speculation about his tax bill during the 2016 election.

In an interview with Fox News, Trump said he did not know where the reporter got the documents and called the publication "illegal" and a "disgrace."

"I have no idea where they got it, but it’s illegal and they’re not supposed to have it and it's not supposed to be leaked," he said.

But Trump stressed the tax documents themselves were "certainly not an embarrassing tax return at all."

He had earlier wondered on Twitter where the reporter acquired the documents.

"Does anybody really believe that a reporter, who nobody ever heard of, 'went to his mailbox' and found my tax returns? @NBCNews FAKE NEWS!"

Trump wrote after the documents were published overnight.

The White House slammed the publication of the document, charging it was "totally illegal to steal and publish tax returns" and calling the broadcaster that reported the story on Tuesday "desperate for ratings."

"The dishonest media can continue to make this part of their agenda, while the president will focus on his, which includes tax reform that will benefit all Americans," a White House official said.

Trump had a tax bill of US$38 million and reported income of nearly US$153 million in 2005, according to a copy of two pages from an individual tax return that was published online by news outlets including network MSNBC.

Trump also paid "tens of millions of dollars in other taxes such as sales and excise taxes and employment taxes," the White House official said.

Trump was the first major-party presidential nominee in decades to refuse to release his tax returns, citing legal advice related to an ongoing audit by the Internal Revenue Service.

- dpa