WASHINGTON (BLOOMBERG) - US President Donald Trump demanded that former Vice-President and Democratic presidential nominee Joe Biden release e-mails and other documents detailing his son Hunter's international business interests in the wake of a New York Post story linking the Bidens to a Ukrainian energy company that figured in Trump's impeachment investigation.

"Joe Biden must immediately release all emails, meetings, phone calls, transcripts, and records related to his involvement in his family's business dealings, influence peddlings around the world, including China and including Russia," Trump said at a campaign rally in Des Moines, Iowa on Wednesday (Oct 14).

The demand came even as Trump is still fighting New York investigators' efforts to get his tax filings and other financial records as part of a criminal investigation. On Tuesday, the president asked the US Supreme Court to block a federal appeals court decision that would permit the district attorney in Manhattan to get the records.

Trump complained at length at the Iowa rally about Twitter and Facebook limiting links to the New York Post story.

The article was based on an e-mail provided to the newspaper by Rudy Giuliani, Trump's personal attorney, whose efforts last year to obtain disparaging information on Biden from Ukrainian officials contributed to the president's impeachment.

One of the Ukrainians that Giuliani met was sanctioned last month by the Treasury Department, which accused the man of being a Russian agent engaged in election interference.

"These e-mails show that Biden's repeated claim that he has never spoken to Hunter about his business dealings were a complete lie," Trump said.

"It was a total lie. He lied to you over and over because he's trying to cover up a massive pay-to-play scandal at the heart of his vice presidency."

'No wrongdoing'

The New York Post never asked the Biden campaign about the critical elements of this story, Biden campaign spokesman Andrew Bates said.

"Investigations by the press, during impeachment, and even by two Republican-led Senate committees whose work was decried as 'not legitimate' and political by a GOP colleague have all reached the same conclusion: that Joe Biden carried out official US policy toward Ukraine and engaged in no wrongdoing," Bates said.

The president has repeatedly alleged, without substantiation, that Biden pressured a former Ukrainian prosecutor to resign in order to block an investigation of a company, Burisma Holdings, that had put Hunter Biden on its board.

It was both US and EU policy at the time for the prosecutor, Viktor Shokin, to be ousted for taking insufficient action against corruption in the country.

"The Bidens got rich and America got robbed," Trump said.

"I cannot sit idly by and watch career politicians like Joe Biden continue bleeding this country dry."

Biden reported to the IRS that he earned US$11.6 million (S$15.7 million) in 2017, his first year out of office. He was long known as one of the least wealthy politicians in Washington, though his and his wife's assets swelled after he left the vice presidency from speaking fees and memoirs.

Unlike Trump, Biden has made tax returns dating back to 2016 publicly available on his campaign website.