Democrats will "never" see President Donald Trump's tax returns, said White House chief of staff Mick Mulvaney on Sunday, as a new front opened in the confrontation between the administration and Congress.

Mr Mulvaney accused Democrats of engaging in a "political stunt" and wanting "attention" after the chairman of the House Ways and Means Committee, Massachussetts congressman Richard Neal, asked the IRS to provide six years of Mr Trump's personal taxreturns and the returns for some of his businesses.

"That is not going to happen and they know it," Mr Mulvaney told "Fox News Sunday."